That's the best reason to start it up before tearing into it like this - a running assessment will point out things like smoking, rough running, low compression, knocking, tapping, scraping or other out-of-place sounds.
The timing chain may be ready or it may not, but it's easy enough to get at with the engine mounted. But this is about the mileage they tend to go, so could be a good time to replace it. And they're cheap, so why not?
I wouldn't worry about any of the bearings, if it wasn't run low on oil they should be fine.
As for the pistons and rings - there's another item that's just so easy to get at that I wouldn't worry. If it's working, don't fix it! I don't see any scraps or broken stuff, so just clean it up, replace the push-rod seals, stick the pistons back in and go. The head gaskets are re-useable, so the whole thing could be torn back apart next week if need be if for some reason you needed to get back in there, without needing to replace gaskets.
Most of these parts last so long, that even if it's got only 20K life left, that's three or four years for most riders. Why get impatient? Spend the money on a good set of tires, or nice rear shocks, or for some better riding gear.
Wanted: Dead, smashed, crashed or trashed gauges
BMW GAUGE REPAIRS - TACH*SPEEDO*CLOCK*VOLT METER *PODs & LIGHT BOARD*