OP - great write up. Thanks!
I did basically a complete cooling system overhaul this weekend with a good friend (@ 85k). Everything went very smoothly, though we did get coolant EVERYWHERE. Once you think you've drained it all, you disconnect another hose and realize how wrong you were! Thankfully the stuff we drained was still nice and blue. A few notes:
1. I personally LOVE the BMW design of the spring clip hose connections. Very controlled, simple and precise. It allowed me to remove and install the rear engine block hose without being able to see it.
2. I consider myself lucky that removing and installing the expansion tank was much easier than expected. It pried off the lower mount fairly easily with a flathead and the new one slid right on. Lower radiator hose too.
3. We did not have a short enough torx socket to remove the screw from the top of the bracket. Tight clearance between the screw head and my headlight assembly.
4. Removing the engine block drain plug is definitely very messy! Somehow my friend fit his breaker bar in there at an angle to get it off. We tried to put tubing in there to control the mess, but it just didn't work
5. I filled the system with just under 8Q of 50/50 after it was all said and done. The manual calls for 8.8Q (<- lol looks like BBQ). Since the car was on ramps, my guess is there was about 0.8Q sitting in the back of the block that hadn't drained.
6. I went with a remanufactured OEM pump instead of the Stewart pump. I don't subscribe to the theory that the Stewart pump is better "because the impeller is metal".
7. I don't like plastic drain plugs and bleeder screws. Though we did not strip them, I was very nervous tightening them.
Thanks to ECS Tuning for having a great selection of OEM cooling system parts. Here is what I replaced:
thermostat (started to stick open @ approx 75k)
coolant temp sensor
expansion tank with new cap, coolant level sensor (old one was metal, new one is blue plastic) and lower spring clip
BMW coolant + distilled water
accessory drive belts
1. lower radiator
2. upper radiator/expansion tank
3. rear engine block to heater core "valve"
4. intake-side of engine block to expansion tank
5. heater core to expansion tank