My knowledge is for a 94 3.2 engine, but I'm guessing if you don't drain coolant from the crankcase you will get some drainage when you pull off the steel pipe.
The pipe seal is a fattish o-ring--I don't know the answer.
I don't have my manuals with me to answer the last two, sorry.

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TomO
94 E320 Wagon, 170k, totalled in 2006
2002 BMW 525i Wagon, 75k
1991 BMW 318is (two of 'em)

I'm pleased to say that my car is back on the road again, thanks to this website... some of my notes might make this job easier for other people:

An allen key can be used as a lock for the fan bearing, but make sure you don't lose it behind one of the pulleys should it fall out of place.

Removing the radiator isn't necessary, but makes the job waayyyy easier. It took me longer to drain the radiator than it did to pull it out. Plus it gives you the chance to clean the front of the radiator too (I found three big dead bugs on the inside of mine)

Removing the water return pipe doesn't seem to be necessary either. I removed the bolt holding the pipe to the fan bearing bracket and then backed off the nut holding the pipe onto the water pump a little to slide the pipe out just a bit, and was able to move the pipe up enough to get a socket underneath and then the bolt in and out.

The bolts on the bracket are not all the same size - the top-left one (looking from the front of the car towards the back) is much bigger than the others, but the rest are all similar in length (but not the same). As you're removing the old bracket, drop the bolts into the same holes on the new bracket so you don't forget which is which.

Those are all the big issues I had... hopefully someone will be able this thread to make their replacement go easier!