Are TFix and Tafferpatch worth the install?

depends on your definition of "worth". I'd say yes, for the overhauled maps if for nothing else - an incredible amount of ugly has been shoveled away.

TafferPatcher_TMA_218_beta and TFix_1.25c are the newest right?.

Yes. Keep an eye out on the pinned threads in the TTLG Thief subforum for the latest updates on TFix (T1), Tafferpatcher (T2), and Sneaky Upgrade (T3).

Any chance you could dumb that down a bit for an old school gamer who just got his first pc in over a decade? Just bought Thief after being introduced to it on PS4 (hear this is much better) and I would like to play it. Currently, the screen is so dark I cant see anything

Just "download a custom patch installer for the right game and run it" is the simplest and dumbest it can get.

And the last time I checked, "old school gamers" were the ones who tinkered with their computers unlike today's kids :P

That is true. But Im talking about a time when hard drives were only dreamt of and floppy discs were the ultimate in technology.