I got a set 19/17 done, superlace - billet hub, excel wheels. Per my conversations with Woody and Zack, they cannot make a 21" wheel tubeless (this the need to order a special built - HP2 front??) but can the 19" and 17" as I have had them do to both mine. Mounted the Tourances, sealed up easy with a bestrest minipump. I had no problems with setting the bead. For the rear they use a 4.00 width rim vs 4.25 as BMW does but it make no difference. Woody said that's the norm and BMW is the oddball on this. If you want to reduce the cost and delivery a bit, call them, as they may have access to a stock set that they can true up or may already have some on their site for sale. If you change your own tires with irons I'd recommend either stay with silver or be sure to use leather or similar when mounting to prevent the scratching. I went with the black (little extra $$ as they have to have these particular wheels colored) to be similar to stock. The can do either a very shiny (spend some time buffing them up) or the standard which is about the same as the OEM black wheels.
"Not all those who wander are lost" J.R.R. Tolkien