8x10 is big for solo use but it sure gives a lot of coverage. Personally I like a catenary cut solo tarp or a poncho-tarp, depending on the trip. I use a bivy so a smaller size works fine. Some folks that go without a bivy like a larger size.
A square tarp works for a hammock but a hammock specific tarp is ideal.
If you're getting into tarps for the first time, a 5x8 square tarp is really fun because you can set it up in a variety of ways- they're really fun to play with! Once you've mastered that tarp, you can get more specific, add a bivy or a bug tent, and move in a direction that suits you.
I wouldn't recommend starting with Cuben or spinnaker. They can both tear out much more easily and you don't want that as you play with tautness, pitching options, etc. Silnylon is a cheap entry point to the experiment and not such a big deal to replace if you go for a catenary cut, pyramid, or shaped tarp in the future.
Have fun- tarps are a blast and a very different camping experience!