If you are just looking to fix some codes, you can do it yourself with the right $15 INPA cable and free software.
If you actually want to "tune" and edit tables, you can do that too, but you need to start reading. I recommend this:
Biggest MS43 tuning thread ever! Incl software... - E46Fanatics
If you want to get a mail order tune, buy a second DME on the Bay, crack the EWS and send it off to someone.
The state of the art in M54 tuning on M5S4 seimens is actually still evolving, but that is all happening in the E46 community. Just keep in mind, they are generally aiming for high revs and their cars weigh half a ton less.
That's the starting point I would use for everything you are asking about.
BTW, oil industry redeployment?