1. To support what? If this is a FOWLR, then yes, that's fine. For photosynthetic animals, it likely won't be sufficient to support them. Do the math--you want to aim for at least 4 watts per gallon for the lower light animals.
2. Lots of live rock--lower maintenance than a power filter of any kind.
3. Need? Nope. Benefit from? Probably. A lot will depend on the bio-load and the water change schedule you're planning on keeping. I don't run a skimmer on my 10, but I do weekly water changes, have only a few snails, some cup corals, a tiny hitch hiker clam, a large hitch hiker bi-valve, a couple of micro stars, some polyps, and one small fish.