PC parts/specs needed for lots of sims at once

I think it's hard to answer this question with specifics, so I'll just share my experience. I'm not sure if it'll be helpful, but maybe ... 😄

My computer stats: 13th gen i9, 64 GB RAM, RTX 4090 (24 GB graphics card) - it's 1.5 years old

I play on the highest settings, use ReShade, have almost 7,000 CC/mod files installed (almost 30 GB), use MCCC to up the lot limit to about 50 Sims (full disclosure: I can't remember if I made this lower because sometimes small lots actually get too crowded and there are no seats or my Sims cannot use objects I want them to use because they're already in use). I have every EP, GP, and SP except Werewolves and Batuu. I have several kits too. I have basically no lag (cooking menu takes a second or so to pop up probably because I have almost 200 food-related mods installed - there's a noticeable pause, but it's very very short). The game loads in about a min.  The main lot I play on is a detailed 64x64 lot valued at $1.1M simoleons. My save file is under 40MB, though. I think FPS is about 150 on a widescreen monitor, but I don't pay attention to that so I could be wrong. I constantly run other applications on a second monitor and I generally don't use more than 50% of my CPU or GPU power with everything going. 

I didn't have issues on my old computer, which is 6 years old either. I don't remember the CPU, but 32 GB RAM, RTX 2080. I did basically the same things. 

BUT there IS NOT any computer that can guarantee this game runs well under stress (huge save file, lots of sims, detailed lot). A lot of people are running into save corruption issues, which seem to be exacerbated by customizing lots, Sims, etc. 

Back of main lot for reference (originally the park in San Myshuno):

kerokerokipper​  If you're still looking for help with this, let me know.  As mentioned above, there's no way to entirely prevent lag, framerate drops, or other performance issues, even on the most expensive hardware available.  The game engine has its own issues.

However, you can help yourself immensely by getting a processor with a high clock speed.  More cores aren't going to help beyond six, unless you're heavily multitasking, because Sims 4 can only use four.  So the speed of the cores matters more than the number.  But absolute clock speed isn't the best metric—you'd need to consider AMD vs. Intel and the particular generation, with newer CPUs getting more done per clock cycle than older ones.

Something like a Ryzen 7 7800X3D (currently $400 on Amazon) would be an excellent choice—when it was released, it was the second-best option for gaming, only a couple percentage points behind the much more expensive 7900X3D.  I doubt the latter or the newer 9800X3D would make a difference to Sims 4.

DDR5 memory is going to help, and it's the only option with the above CPUs, but if you go Intel, make sure you get a DDR5-compatible motherboard.  You don't need more than 16 GB RAM for Sims 4, but if you want more, that's not a bad thing.  Above about 6000 MT/s, the first-word latency matters more than the absolute speed.

For the graphics card, Sims 4 won't benefit much, and probably not at all, from anything above an RTX 4060, unless you're playing at a high resolution AND a high refresh rate.  Even my RTX 2070 has never been maxed out in the game.  On the other hand, if you want to play other, newer games too, they may benefit from a faster GPU.

For storage, any NVMe SSD from a reputable brand is not going to be maxed out under any Sims 4-related load.  So figure out how much storage you need and buy one or two drives that fit.  Even a (significantly slower) SATA SSD would be fast enough for Sims 4, but they're typically not much cheaper than NVME drives these days.

Aside from that, don't cheap out on the motherboard, and absolutely do not get a low-quality power supply.  A bad PSU can wreck your entire computer, literally.

If you put together a parts list, or you find a prebuild that you like, feel free to link it for a second opinion.  As far as pcpartpicker is concerned, I wouldn't absolutely trust every detail on the site, but it's at least good about the big picture, for example not listing DDR4 memory for a CPU or motherboard that only supports DDR5, and vice versa.

I'd love your help if you wouldn't mind? My budget is a bit lower, ideally €1100 or less ($1300).

https://ie.pcpartpicker.com/list/jcPtfd

The case I am looking at is about €60 so that build is currently standing around €1020. 

I could stretch to €1200 if you thought the upgraded parts would make a big difference. Perhaps 2TB SSD is overkill and I could save some money on a 1TB version to put towards something else?

MaireadDeevy​  I like the build you've put together, and the only thing I'd upgrade is the graphics card, IF your budget could accommodate it.  But the rest of the build would support a faster GPU later too, so you could upgrade in a year or two rather than now.  And Sims 4 doesn't strictly need anything faster than a desktop RTX 3050; this would more be for other games, or for adding ReShade or something else that makes Sims 4 more demanding.

This RTX 3060 is in stock and only marginally more expensive than the 3050 you've picked out:

https://ie.pcpartpicker.com/product/KXYmP6/asus-geforce-rtx-3060-12-gb-dual-oc-v2-video-card-dual-rtx3060-o12g-v2

And this RTX 5060 is only a bit more than that:

https://ie.pcpartpicker.com/product/xNy8TW/asus-dual-oc-geforce-rtx-5060-8-gb-video-card-dual-rtx5060-o8g

As for saving money, you could go with a high-end tower cooler rather than liquid cooling for the CPU, which won't generate that much heat.  DeepCool isn't a great brand for liquid cooling, although it shouldn't matter for this particular CPU.

And you don't need a 2 TB SSD, so yes, you could save a lot of money there.  If Sims 4 is the only significant source of data you'll store on this computer, even 512 GB would likely be fine, so one terabyte should be more than sufficient even if you never delete your old saves.