Liking the Merc. In an R you can have fun in all weather and road conditions and not murder your tyres😂 have a look at this as a start.
Some VERY Basic info to set you away - off the top of my head;
The Mk7 had c. 300 bhp. Analogue instruments. Twin tone cloth seats Standard for a quick guide. Up to 2017. 3dr. 5dr. 6spd Manual or DSG. Wagon also joined in.
Mk7.5 brought external bumper facelift, arguably looks more “aggressive” Virtual digital Instruments, dark coloured cloth seats as standard, 310 bhp, 7spd DSG, 6sp Manual, 3dr, 5dr and Wagon. These are seem as the easiest to tune.
2019 Mk7.5 GPF Filter (WLTP compliant) 300bhp , most with some additional features as standard, but check carefully!. (Reverse camera, keyless entry/go, lighting upgrades) 3dr phased out. Also Manual transmission. So Wagon and 5dr hatch till end production run. GPF fitted can make tuning much less straightforward
Popular options, 19”Pretoria Alloys, DCC (dampers.) Dynaudio, Leather Seats, Panoramic roof, Nav and Infotainment upgrades, Heated screen etc.
Some useful guides too to watch on “yoochoob” like Volkswizard.
Get researching. Use the Search facility on here. Come back to ask questions when you’re stuck.
They are Superb all rounders - but get a good drive in a few different types to help wet your whistle too. Good luck with the search😀 and I’m sure to have made some detail mistakes or slight inaccuracies....but you get the idea.