It's pretty hard to get extra HP out of the M52 /M54 engine without going with a turbo or supercharger.

You can put an M54 crank and ZHP or Shrick (I think) cams in your M52tu, and the larger M54B30 intake but you will struggle to get it tuned right in your '99328i.

My suggestion is to get the M52tu engine as stock as possible and leave it alone. Replace front and rear suspension on your 328i, get it's interior and exterior looking good and drive it like you stole it.

Unless your M52tu consumed oil, I would not replace piston rings. I know I recommended this in your other thread, but I thought you had an M54, which has a worse piston ring design than the M52tu..

I would in your case:
1. get the head fixed/valves tested by a machinist
2. time-sert the block
3. clean everything.
4. replace cooling pipes (OEM only)
5. replace timing chain guides
6. loctite or wire the oil pump nut
7. replace vanos seals and maybe the rattle rings
8. New front and rear main seals.

 

Yea my car was consuming like oil crazy but i didnt really notice until i pulled the head, i found this kit online that basically goes through everything i want to do before a turbo.

https://k64performance.com/strona-glowna/4702-engine-kit-stage-3-m50-m52-m54-maxboost-500-1000hp.html

other than everything on this kit im also gonna do headers, b30 manifold, and a full tune. (Maybe injectors depending on what the tuner suggest)