Some questions about modding and updating

So, even though I joined this stuff in 2017 or something, I have little to no experience with modding GTA V, because back then I realized my computer was terrible and couldn't handle anything, then I realized I forgot to make a backup copy, so I panicked and undid everything. Then I forgot LSPDFR existed for two years, played GTA Online, realized you don't play GTA Online, and decided to get into LSPDFR because some jackoff decided it was funny to make the Oppressor Mk II 50% off on Black Friday.

I was actually about to finish modding my copy this week. Then, on the day I decided to start replacing cars, Rockstar Games announced they would be adding Franklin Clinton to GTA Online literally next week, so now I'm just waiting for that to happen before modding. I had a modded copy with LSPDFR and RPH installed, and I deleted it about an hour ago.

Anyways, a few questions that I couldn't find the answers to on Google:

• A few posts I've found seem to imply that the contents of each update are located solely within the update.rpf file, and updating a modded copy just requires you to replace the old update.rpf with the new update.rpf. Is this true, or would I need to fully replace the modded copy? Basically, how would you go about modding a duplicate copy of the game? (the big question here)
• I used the LSPDFR uninstall file to uninstall LSPDFR, but simply deleted the modded copy to remove RPH. Did I break anything?
• Are relatively minor mods such as car replacements and sounds affected by title updates? What mods would I need to wait to update, aside from requirements like LSPDFR, RPH, and SHV?
• What's the difference between EUP, EUPFR Basic Configurations, and EUP Menu? Do I actually need any of those, or is the default uniform customization enough?
• Does LSPDFR work on an incomplete save file? I currently have two save files (one is my first save with Story Mode completed, the other is my newer replay that's around the middle of the game), and I'm wondering if my actions there would screw with things like missions, random encounters, or character stats.

Thanks in advance.