Reset - Since I was changing oil more often than the car wanted me to, and I didn't want to mess with the Inspection I and II intervals, I didn't reset after changing the oil. Conversely, the one time I observed the "change oil" indicator, I simply reset the light without changing the oil since I had my own cadence. I used a Peake tool to reset the light and also retrieve codes when they occurred.
Oil - I tried to use BMW Longlife oil from the dealer, but the stupid dealer only carried 5W-30 and would not order 5W-40. Surprisingly it was only $3.97 per quart with my BMW CCA discount (I used it over the winter in the 5W-30 weight). I tried using Mobil-1 0W-40 once and that was OK, but I mostly stuck with Castrol Syntec 5W-50.
Cost - 8 quarts of synthetic ($5+ each) plus $8 to $10 for a Hengst OEM filter means I usually spent around $50 just for oil + filter when changing oil myself. So I see $80 as "in the ballpark" for what dealer might charge. (BMW started requiring synthetic starting in MY99).
Changing my own oil - I always changed oil myself and never encountered much difficulty. The only trick is to remember to crack open the oil filter canister before opening the oil pan bolt so that the oil filter canister oil drains out with the rest of the oil.