Older low end PC, can I run all dlc on these specs (or at least add catsdogs)?

@Lightsims8  Stuff packs have a negligible impact on performance, and kits even less than that, so I'd say load up on both of these to your heart's content.  Most game packs have a low impact, although the newer ones (Realm of Magic and onward) have a higher impact than the older ones.  The oldest three expansions—Get to Work, Get Together, and City Living—are comparatively low-impact too, although they're more demanding than GPs.

Cats & Dogs is probably the single most demanding pack, and I really can't tell you whether it will run well or not.  It's possible this one pack will push your game over the edge, or that it will be okay but you'll be close enough to the limit that adding more EPs isn't a good idea.  There's enough variation in outcome from one player to the next that it's impossible to make predictions, other than when someone's machine is above the requirements for ultra settings.

In your position, if you really want C&D, I would buy that alone, install it right away, and see how it runs.  Send a sim to Brindleton Bay and get a bunch of strays on the screen at the same time, then see what you think.  Download a larger (but not massive) house from the Gallery and place a sim and pet inside, and play with them for a while.  If the game is bogged down, you might be able to get a refund from EA customer support, although I wouldn't count on it.  You could simply disable the pack and come back to it if and when you get a new computer.

Dream Home Decorator is somewhat broken, but not really in a performance-related way.  If you're interested for the CAS or Build/Buy items, it's fine.  If you want your sim to be an interior decorator, you'd probably run into some trouble on any machine.  But it shouldn't seriously impact how the game runs overall.

Regardless of your decision regarding C&D, I would say add expansions newer than C&D one at a time, testing along the way to make sure performance isn't starting to drop below what you find acceptable.  Buy all the SPs and kits you want, in one go, and test that content too.  Buy a few GPs if you'd like, but not all of them, and test before adding anything else.  You have some time; the spring sale ends March 28 at 10 am Pacific, according to the fine print on this site:

https://www.ea.com/sales/spring-sale

Thanks alot for your help @puzzlezaddict  , I was worried cats& dogs might be too much for my system, I don't really need it, just thought it would bring cozy feel to game, but I can skip that one till I get new PC at end of year or next year.

I'd seen the end of sale 28th date, but was confused & thought it might be 23rd, since if on ea website & click sims logo for home page, says 23rd, so I was nervous the 28th date was incorrect, so wanted to buy by 23rd in case.

I only wanted dream home decorator for the build items, so I'll get that one, thanks for heads up on the broken gameplay, I won't need to play that career in case. 

I'll probably get few more stuff packs too then, & bust dust; I want vacuums for clutter look realism, but don't like dust bunnies I think they're creepy, lol, wish it was just dirty floor & could turn dust bunnies off. I hear there's sparkles after cleaning, do you happen to know how long sparkles last, sounds annoying, wish could turn that option off. If it lasts more than a couple sims hours, I'd turn off option for btd gameplay in options, & only turn it on sometimes when in mood to play, if that's the only way to be rid of sparkles.

I could try get together & city living, if only for drain pipe & heating duct items :D really its the only reason I'd want them, not fond of heights, or cities, I'd rather country side look, & introvert play so get together not my thing. But those couple simple items for realistic look is my thing, couldn't find those 2 items anywhere as cc, plus want to play without cc for a while, or if I add some, want minimal very important, & updated trusted ones, I had many cc before, but game would crash alot usually in only 2 mins of gameplay with family & toddlers on lot, even if house or family size not too big. CC's only good for me for pictures of builds & sims then, but I want to play too, that's why I'm trying to add more dlc to make game less boring of seeing same old limited amount of stuff when I had only base game & gtw. Game is much better already with what I newly added, especially seasons, now I feel motivated & excited to play again, I've barely went on sims for years, I missed it. 

Another question: @puzzlezaddict 

Horse ranch & cottage living is only tempting for the country or cozy decor items, but I'm concerned about the animals being on those, do you think it may be harder on system like cats & dogs?

@Lightsims8  I haven't seen any evidence that Horse Ranch is as demanding as C&D.  What is abundantly clear is that 4 GB RAM isn't enough to run Sims 4 well anymore, but 8 GB is enough if you don't run much else at the same time.  (A lightweight app like Spotify should be fine; a dozen Chrome tabs or the Discord app might not be.)  Cottage Living had major problems at launch but now seems to have an impact on the level of Seasons: clearly more demanding than early EPs or any other pack type, not as bad a C&D.

However, the effects do stack, so take your time in adding more content, or be prepared to disable certain packs if the performance hit is beyond your limit.  You also don't need to complete your purchases during this sale.  Going by the pattern of the previous five years or so, there will be multiple Sims 4 sales between now and Black Friday week, likely with the same prices as you're seeing now.

You can also avoid the effects of the animals by not having animals in your game, at least not now.  It's not like your sim is going to adopt a horse or llama behind your back, and the only inactive sims that own them by default live in the worlds that came with these packs.  There's no reason the Build/Buy or CAS items should have any negative impact on gameplay.  I would be a bit careful with the animal-related lot traits from CotL—that's not to say don't use them, only watch for negative effects and be prepared to remove them if necessary.

The dust from Bust the Dust seems to work in a way that no one likes, so I'd suggest shopping around for a mod that allows you to control the effects.  I know there's at least one popular mod that's been in use since the kit was released, and while I haven't tried it myself, other players say it's exactly what they want.  And you can of course simply disable the feature in-game and keep the vacuum cleaners.

When you're ready to buy a new computer, feel free to ask for help with that.  Whether it's advice on components, suggestions for specific models, general hardware talk, or just a second opinion on the unit you've already picked out, we're always around to answer these kinds of questions.

" It's not like your sim is going to adopt a horse or llama behind your back, " XD

Thanks again, helpful advice, & I'll for sure post on here again when it's time to get a new computer end of year or next year, it'll be gaming PC on sale & should be fine, but I might need advice between 2 choices when that time comes 🙂 @puzzlezaddict 

(Just adding here; I got bust the dust & dream home decorator last night, seems OK so far, tried a very very cluttered 2 story house with full basement too, with adult, child & 2 toddlers, in a new save game where all 4 towns are untouched -meaning I left their pre-made houses & sims there. On my other save I'd been testing, I had removed every house & sim, made a one lot sim with only alot of furniture & clutter on lot to test with before I build. I like making my own town from scratch.- Anyway, the smoothness of game play wasn't too much different, but I did have a few moments of laggy gameplay with that bigger family; they didn't last too long, only at begginning when 1st loads: 1 was welcome wagon, other was when I load the lot again with nanny still on lot while father is at work as cop. I load again when he's home & she's not there & it didn't do it, don't know if it's issue with nanny or performance issue. It made CPU go up from usual 35 or 50, to 65 or 69 for about a minute, but goes away & runs fine after.)

At least it didn't crash or stay that way, so its fine. Just in case, I'll take that as a hint to stop adding until my new PC..(except for 1 more, I want dine  out, hope it's OK 😉 )

@Lightsims8  Dine Out should be fine in general from a performance standpoint.  But restaurants have their own issues, and if you get one to work properly, you might see a performance hit from having so many sims on the lot.  You might test other situations of many sims on one lot, for example going to a community lot at peak hours and counting the sims as they arrive.

I wouldn't worry about the CPU use spiking the way it did; the only issue is the drop in performance.  I'd also suggest turning off dust, as an experiment, just in case your graphics chip is having trouble rendering the dust or the sparkles.