Q5 Pro won't be much more expensive than Q5 4K3D. It is more powerful hardware and supports the latest formats (4K60, 10bit especially), which will be increasingly important.
I advise waiting for Q5 Pro.
1. Yes, but there isn't much 4K30 or 4K24 material.
2. Yes. as above.
3. It either won't play, or it will play very jerkily.
4.
5. Yes, they play well.
6. No trouble. It passes 5.1 audio excellently from all codecs.
7. It's not great for games but most/all games will run. H8 is better for games, it's more powerful.
8. For games, yes. For video, no. Video format support and quality will be better on Q5 4K3D / Q5 Pro.
9. Yes.
10. Yes. 4K30 / 4K24.