Hi there, I am also looking at Reaper as an alternative DAW in light of Sonar's situation. Love Sonar, but I'm really starting to like Reaper right now. it's only been 4 days, but I feel like I'm ready to make the switch.
As for the VS700, I was able to get about 30-40% functionality. Right out of the box, the transport, track faders, pans, track mute/solo/arm, and jog/shuttle wheel all work once you set the control surface as Mackie. Then, through the actions lists you can assign any action in that list to a button on the console. Most buttons. Some aren't coming up such as Save, Undo. So all of the edit buttons can be mirrored exactly, and some of the View buttons. Then, others are already assigned to different/weird functions. For example the fader views buttons (track, buss, master) all assign different automations to a selected track, which is not really desirable for me. Lastly, the track levels don't light, and the fader banks don't switch so looks like i'm stuck with just 8 plus the master. At least, so far.
However, I have literally only spent about 30 minutes on this. I'm sure there is more to discover on this and that's what I like much about Reaper so far. Setting up what I have so far has been pretty darn easy, and with the functions I have now I can run my studio pretty well already.