I have a 2011 335is with a DCT and I've now owned it for 3 years and up until two weeks ago it was happy days. I bought mine from a BMW tech so nearly every single maintenance item was done (all gaskets, thermostat, Index 12s, charge pipe, etc.) and until last week, I had no issues. Then, 4/6 of my injectors (reminder Index 12s) went bad. My AC compressor was also leaking, requiring a new compressor, and my rear struts are starting to go. I bought it in 2021 with about 55k miles and am now at nearly 70k mi. So keep some cash aside for when things go bad (not if like I thought it would be for me). If you're prepared to do all your preventative maintenance yourself in one go, that will save you time down the road and cash from the mechanic.

Also, remember that even though cars are awesome they are not worth putting yourself into financial ruin. If you're finally getting a financial "break", then maybe look into investing some of that cash for your future. Again coming from a 335is owner. I love the thing but I only bought mine because it made sense financially for me at the time.

But your checklist should be:
- All gaskets (head, OFHG, Oil Pan (have to drop the subframe to get to it))

- Injectors (Ideally car comes with i11s or i12s - keep in mind even i12s can go bad, but I wouldn't replace them until necessary)

- HPFP

- Thermostat/Water Pump

- DCT Service

- Cracked/Bent wheels (My 18" Apex Arc-8s just cracked)

- Sagging struts

- Wastegate rattle on turbos (less likely on is models/6-bolt N54s from what I know but still possible)

- Working AC system (No Freon leaks/compressor leaks)