Most of the readily accessible fittings - fairing, muffler, etc. - are stainless steel internal Torx buttonhead screws. Thus, you'll need several Torx drivers, T25 being the most common. You can get either screwdriver type or 1/4" drive socket-type drivers. Going deeper, a set of 3/8" drive metric sockets, ratchet driver, breaker bar. There are few fasteners (I think) that won't be dealt with by the sockets and a couple Torx tools. These are inexpensive but get quality stuff so you aren't left hanging when/if it breaks (as I have had happen). DON'T go to Walmart and get Stanley brand anything. Although in days gone by they were a respected name, that is in the past. Sure, you can get by, but don't say you weren't warned. Craftsman, and the stuff from Lowes or Home Depot is pretty good. Snap-on and Mac are reedonkulous expensive and made by the same Chinese factories that make other brands. Sometimes a good deal can be had buying used stuff on craigslist, ebay or similar, if you carefully inspect before you buy.
A torque wrench is handy if you're a careful sort, or don't trust your calibrated arm; the 3/8" drive type is what I'd suggest, click style or beam type is up to you, cost is significantly different.
A set of tire irons plus rim protectors will be useful, also a means to break the tire bead, IF you plan to change your own tires. I used a 11-foot section of 1.5" pipe with a chunk of 2x4 to break the beads on my tires.
If you plan or expect a dive into the clutch, there are a couple BMW-specific tools but sometimes you can borrow those.
A factory (or copy of) the rep-rom is good, but be aware that it's apparent only function is to take stuff apart and put it back together in the approved sequence. There is nearly nothing on it for diagnostics, or functional descriptions.
A bookmark to the factory parts diagram, specific to your VIN, should be on your computer/phone. Knowing the significant parts suppliers is handy, though prices don't vary much.
After the above, a bit of elbow grease is always useful. You won't need blinker fluid or smoke to refill the electrical system. AFAIK
the electrical systems were pretty sorted AFTER 2009. Make sure the bike you get has had all appropriate recalls performed.
Others will chime in, bring it on, I'm listening too.