Yeah. That's the same thing I'll have to do. I just did the coolant last week and new bmw battery.
I love the 03 e53 4.4 one of the best cars ever made.
I'm also looking into getting my rough idle fixed trying to figure out what it is.

Easy stuff, just use the articles above to provide an overview on DIY as everyone has been there and done that before. Getting a good baseline of your vehicle will help you with peace of mind at the minimum.
General Service
Oil Changes frequency of the changes is probably more important than anything else. Lots of postings in that dept on this forum.
Oil/Air/Cabin Pick OE, Mann
Plugs 4.4 use the NGK fine wire ones - Iridium IX Spark Plug NGK BKR6EIX
Part Number: 739-BKR6EIX.
Fuel Filter (don't forget this one!)
Brakes- Flush fluid if pads are ok.
Tires - Balance them!
Suspension- X5 eat thrust arms, use the HD Meyle or research the Poly versions. At 100K everything is on the way out. Better to do all than to do one part at a time.

Detail and wax often. Smile as you drive! :thumbup:

There is always more to do.....The forum is here with tips and ticks and a few off hand remarks anytime.

Thanks a lot for the tips. Yeah I like to do things my self just like you said to know your car. Every out car I had did most of the work, unless it's was some crazy shit lol.
This page is awesome thanks bro