1. Cat 6a through conduit
2. Yep, all ran to a central point
3. Wire for 7.1, then figure it out
4. It's conduit. Electrician can do it.

I would also run conduit from your attic to a central location. Run conduit from central location to every room, too.

I would put in a central vac system. If you're in Utah, Reed's Built-ins is the way to go. They can also handle all of your conduit, cabling and everything. Talk to Erik. He's the most knowledgable guy in the industry for home AV and central vacs. They would give you better info on "future proofing" your house than anything you'll find here. That's all they do and they've seen it all.