Wow, that's a nice computer. And sure, it's overkill for TS3, but you never know what else you'll want to run on it. Besides, those ROG Strix graphics cards are just so pretty.
Right, you had some questions.
1) My account has four base game codes, or rather three standalone base game codes plus one from a combo pack, for reasons. It's fine. But definitely add the Steam code to your account, or you might have trouble getting your store content to work, since it's encrypted. When I reinstalled via Steam, I had no trouble downloading what little I had in my purchase history.
Also, be sure to redeem your extra points for registering the new base game and World Adventures. Last I heard, the offer still worked.
2) I've seen some guides that are kind of overdone, or not too helpful. I can try to find a better one, if you want. Or, if you send me the device ID of your graphics card, I can send you instructions. (This is usually better done by PM, since the specifics are dependent on the card.) The device ID is in a lot of places, among them the deviceconfig that TS3 generates, about 35 lines down. For example (ID in bold):
Chipset: Vendor: 1002, Device: 67ef, Board: 0179106b, Chipset: 00c0
3) Even though you didn't mention it, it's critical that you take steps to limit your in-game frame rates. A 2080 will throw rates well into the hundreds if fps isn't capped, for best results to the refresh rate of your monitor. For Nvidia cards, the usual first tool to try is the built-in Control Panel. But it doesn't always work, and never works in windowed mode. So if you need it, you can download Nvidia Inspector, or RivaTuner Statistics Server (both free). Unlike the others, RTSS does need to be running in the background to work.
To see your in-game frame rates, bring up the cheats console (crtl-shift-c) and enter "fps on" without quotes. The number will appear in the upper right corner of your screen. ("fps off" makes it disappear.) Here are screenshots of the settings for CP and Inspector:
https://forums.thesims.com/en_US/discussion/comment/16540301/#Comment_16540301
I can grab one of RTSS as well, if you need it, although it's pretty straightforward. Keep in mind that to set up the game's profile for a Steam install, you'll need to use TS3W.exe, with the W, unlike an Origin install, where you'd use TS3.exe.
And I know what you mean about the emotional impact of seeing TS3 running again. I almost teared up when I got my Windows/Bootcamp install running a bit more than a year ago, although that was because of all the packs I finally had that I could never play in macOS. It's amazing how much this game can still mean, a full decade later.
