Any reasons for CAT & sound in bathrooms?
Only if you ever want sound there. Again, since wire is cheap, if it's even a distant possibility, run the cable. I don't plan on ever putting a TV in my bathrooms, so I just ran audio. Will be nice to listen to news in the morning while getting ready. And the SO loves to blast music while she's getting ready to go out. So it will be great for her.
I haven't finalized where to put the AVRs, but my current plan is to have them local as well.
If that's the route you're going, you should definitely go with the Sonos connects. With these, you can play each zone independently or play them altogether. Or 2 on 1 station and 1 by itself. Really easy setup, too.
The builder said they are using cat5. I'm not sure if that meant 5 or 5e, but I assume I would want 5e?
At least 5e, if not 6. It's slightly more expensive to go the 6 route but it future proofs the house. However, 5e should be more than sufficient.
And again, if your budget allows, you should look at running everything to a central closet. Will be more expensive once you start looking at whole home control options, but aesthetically, can't be beat. My setup will have 1 AVR, a couple DirecTV genies, blu ray player and audio device all in one closet. From my iPhone / iPad / Galaxy S3, I'll be able to turn on any TV in any of my bedrooms/LR and switch to any of the sources or play movies/music from my NAS. It's definitely more expensive than a few Sonos connects, but there won't even be a DirecTV receiver or Blu Ray player near any of my TVs. Just the TV hanging on the wall.