Can everything within the downloads folder be simply copy and pasted from one computer to another and start working as expected? Aside from things like CEP, custom camera configs, neighbourhoods etc. Will the files that modify gameplay copy over without issue or do they carry remnants of the previous game they were being used for? A bit late to ask this as I've already transferred everything. Everything seems to work as intended, but I know how errors in TS2 can lay in wait for months before showing themselves.

Anything that doesn't require special installation - you know, files put somewhere else than Downloads (example: catalogue hiders that need files put in the game folders, objects like stairs which you use Scriptorium for (or do manually)). You can transfer neighbourhoods - just stick the folder in the new neighbourhoods folder. I just copy-pasta camera mods if I do a reset - no problems there.

What I thought then. I was mostly worried about mod files (like for example BOs) and registry issues. Thanks.

If you are installing by single disk you must patch them as you go because most mods are for the patch version of the game.