I hope this is on time before your trip. I've got a pile of GPX routes that I could pass on soemhwere this week if you're interested. As far as our trip was concerned: it was lots of fun, despite the intermittent rain and low temps. The weather made a lot of the trails a bit slippery as well, but we're used to dealing with this.
Except for the last day, we rode directly out of Selva, on the eastern end of Val Gardena. The scenery is really spectacular ('classic' Dolomites landscapes). Due to the afternoons being filled with showers we generally took lifts up to 2000 m to save an hour or so of climbing on gravel roads. Lift access is pretty good, and in Val Gardena the majority of lifts don't charge extra for taking a bike.
The tourist office and various GPS sites have recommended routes (a booklet of 25 is available for €9 or so), which for the most part are gravel roads (although some quite rough) interspersed with some neat singletrack. In general the routes prioritize on spectacular scenery, not spectacular descents, so we ended up modifying the routes a bit to increase the amount of singletrack. Most of our riding was in the direction of Val Duron, on the southern edge of Peuz-Geisler park, and Alpi di Siusi.
As the place we stayed gave us free guide access, we did the Sellaronda lift-assisted tour as well. It's a wake-up-early group ride with one or two guides, and takes about a day. The clockwise route (from Selva to Val Badia, Arraba and back up along Fal di Fassa and Canazei) is the more interesting variant. The last day we'd planned a ride from Arabba to Cortina and from there a traverse of the Senes-Fanes park. I'd been there before and it's a wonderful riding spot. The ride started with that perfect combo of technical trails and mind-boggling scenery, but we had to cut the day short after what initially appeared to be a serious fall. I'm pretty sure the remaining portion would have made for an epic ride in all senses of the word.
On a couple of days we had lunch at a mountain hut - although far from cheap the food and service are generally very good, and nobody objects to you walking in covered in mud. You do need to take care with hikers, though. Although very friendly for the most part, the sheer volume of them means you absolutely cannot go full throttle.
Also, I'm used to getting a topo map and picking out the singletracks. For some odd reason the Italian Tobacco brand maps aren't as suitable as the IGN ones I used in France. Sometimes 'gravel roads' ended up in brutal tracks, while 'narrow hiking trails' almost felt paved over. If you have the opportunity to get a guide for free as we did (or at least at a decent price), give it a try for a day or two!