Best advice is to keep it stock until you are familiar with the systems, the vehicle and the service literature.
A lot of people buy one and get in over their head because they thought stuff was easy, and did not plan their "mods" properly.
You will read a lot of their stories here, and like all fora, they come and go, usually when they leave they are beaten and hostile towards the vehicle / brand simply because of their own sheer ignorance.
No different in VAGworld or BMWland either. But the learning curve with Mercedes is a harsh one. Either you get onboard with their factory service manuals and EPC/WIS, or you will pay through the nose and end up throwing money at a problem because beligerance took you there.
The factory service manuals and EPC are very thorough. Yes there are always alternative means to achieve a similar outcome, but the factory way is actually the most efficient in 95% of cases.
Hold off on your purchase and wait for the best condition vehicle you can find for your budget. a W201 is no longer a cheap car to own and service. But it's certainly a better car than the 202 or 203, and if not for the 204's electronics and the c63AMG, I'd almost say the 201 is better than a 204 as well.
Keep looking for that gem. They are out there. Good luck.
1987 201.034 - € spec 5sp. Blauschwarz- Hermann.
1992 124.051 - 6sp man. Iceblau - Gretel
1992 124.090 - 4sp auto Malachit Grün - Beatrix
1987 107.048 - 4sp auto Signalrot - Stella
2012 212.074 - 7sp mct-speedshift Diamantweiß - Klaus
exit lounge: 1989 201.035, 1987 201.029, 1987 126.039, 1972 107.023,