a few questions

I recently had to uninstall my sims due to a problem and I have reinstalled up to University. I had to borrow my cousins PC version because my DVD for the original Sims 2 is busted somehow.

My questions are:

Thanks for reading I never understood the whole "putting back, the backup files you saved" part. I understand the back up part: To backup your game you backup the The Sims 2 folder in your EA Games folder under your My Documents correct?

1. If I put all other expansions I own + stuff packs up to Freetime (including Kitchen and Bath) then add Celebration would it ruin the game? I don't own Celebration but my cousin does (I think) I need to get it from her and I wanted to know before I borrow it. If I ever have to install my backup do I back up for just the one I'm playing on? or for all users?

2.I backed up the original game (not with university and with no CC yet at all I want to install all my games first]. Once I have all of them installed and have JUST the original back up saved will it just do the original files only and non of the expansions if I overwrite the The Sims 2 folder under the EA Games? Would you recommend backing up right after all of them are installed with no CC? then delete the one I made originally?

3. How to you refresh the game is it just overwriting the The Sims 2 folder (and all contents) under EA Games in MY Documents? If so will it get rid of all my people? If so that's okay as long as the game would be fresh without having to reinstall everything.

4. if I back up all my games till freetime (The Sims 2 file in my downloads), then I got Apartments but I have CC in. do I need to reset the game by using my backup I have before then install Apartments? Would it get rid of all my stuff? I'm so lost.

5. Do you know if they stil lsell the PC version of the original game without the Double Deluxe? Also, what happends if you delete the group.cache, and what does it do?

ETA: Are these hacks okay to use without messing with the game's files too much? As far as I know they are but I want to double check.
- Inteenminator
- InSiminator * I know this is okay
- Freetime Aspiration Critical Fix
- Triplets & Quads
- Neighborhood Camera Hack that let's you move everywhere
- CEP
- Buyable Maternity Clothes Hack

ETA: Can I also just save certain parts as well such as downloads, neighborhoods, etc for two users me and my mom?