1. I'd go with the 39 because there are more useable gearing options with the rear SS

2. On a fixie 70 gear inches is pretty good for hills. I would go a bit lower with SS

3. No need for a tensioner, and no advantage from running one when you don't need it. just adds weight and drag

4. Drops are fine. They have all the same advantages n a ss that they do on a geared bike. Some people just like risers.