1. I'll buck the trend and say 52. With spacers and a cog, chainline is adjustable, so that's not a factor. And with a cog, you can easily go to 25t, which will let you spin your heart out. Also, more chain = less chain wear. Furthermore, bigger chainrings look badass, regardless of how big the cog is.

2. I'd say a 19t cog would do well. 52-18 would be my choice on a fix, but you want to gear down a little, since you can coast.

3. Tensioners are lame, don't use one if you don't have to. And you don't have to. Chain tugs, on the other hand, may prove useful, especially with a QR hub.

4. Keep your drops and both brakes, especially if you're already used to it. A plethora of hand positions is always good.