Yes there quite a few things to look for, just off the top of my head:
I am guessing that this has already been cafe-d, and if not, still take a good hard look at the wireing if it looks like it has 9324050 boxes of connecters and tape holding it together then your looking a a big headache latter.
Let the bike run for a few minutes and look at the push rod seals (on top of the cylinders, there black, two per side) and the cylinder bases are they leaking?
Look at the little shelf under the bell housing (clutch housing, where the trans meets the engine) is there a puddle of oil?
With the bike not running and in neutral, push it forward and back a few feet, does it roll smooth or is there a clunking or fighting in the rear end or drive train?
If it has a aftermarket electronic ignition, buy a set of points and a condenser for it and keep them under the seat. It will fail, and as always, in the rain, at night, in the middle of no where.
Look under the exaust pipes, are they rusty?
Aside from the usual stuff, thats the best I can think of. I dont own a bmw, just work with them. I am sure some of the air head guys on here will chime in with whatever I forgot, over looked, or just don't know.
Good luck