Thank you all for your comments!!!
A few notes:
1. Regarding the computer specs, I am thinking of maybe upgrading some of the parts, but it may take me some time (and in any case I will post in the technical forum). I was looking for solutions to implement as of now.
2. I have reinstalled all (/most) of my store content in the last few days,I want to update that I actually did managed to install specific items from store worlds- it is a little manual but it goes like this: I installed the world, then, in launcher - installed content- I deleted the world , it important to delete the package of the world first (I think i manually deleted from Installed worlds folder, too). Then I manually deleted from launcher all of the unwanted items from this world. Since I reinstalled all content and the worlds were pretty much at the begining it was easier, it is more difficult to locate items from world wheb there are many items installed. And so for example from Midnight Hollow I kept like a few dresses, a few hairstyles and the Cashier objects. I did this with 2-3 more store worlds.
3. I finished installing all store cc and other cc (using pre saved .dbc files), then ran one of my heavy saves. It actually worked pretty good!!! Imprtant note is that I ran this save with almost no mods.
4. Which bring me to the next question: I wish to convert most of my package files into sims3pack (I know most simmers actually prefer the opposite). I found only one tool to do that, which was not successful, and I can do this also with TSRtool but some items will not open there.
