@Ephendrielle I'm so glad you're figuring out how to use mods. I started using them myself when my games kept glitching out and becoming completely unplayable, and I've never looked back. If you ever have specific questions about NRaas mods, you can also ask on the website—the current developer and admins still support the mods.
Since you have a gaming computer (and a gaming graphics card, from the sound of it), you may need to take steps to limit your in-game frame rates. Unlike most newer games, TS3 doesn't have its own fps limiter, and a strong card can generate high enough rates to damage itself from overwork over time. More immediately, you might see weird screen glitches, although that doesn't always happen. To check your in-game frames per second, open the cheats console (crtl-shift-c) and enter "fps on" without quotes. A number will appear in the upper right corner of the screen, and it should never go above the refresh rate of your monitor. ("fps off" makes the number go away.)
To cap fps, you'll need to use an outside tool. For Nvidia cards, the first choice is is the built-in Control Panel, but it doesn't always work (and never works in windowed mode). The next tool to try would be Nvidia Inspector (free download). With Inspector, you'd need to explicitly set the fps limit to the refresh rate of your monitor, which is normally 60 Hz. You can find screenshots of the setups for both tools in this post, under the spoilers:
https://forums.thesims.com/en_US/discussion/comment/16540301/#Comment_16540301
One note: For an Origin/1.69 install, you'd use TS3.exe to set up the game's profile in each tool, but for disc or Steam installs (both on patch 1.67), you'd use TS3w.exe, with the "w."
