Greetings from Classic and Vintage! I recently put together a Free Spirit 10-speed (horizontal dropouts, freewheel hub, etc.) and decided I don't like it, so I'm going to turn it into either a fixed gear or a single-speed. I've read over all the links, but I still have a few (possibly stupid) questions:

Is there a difference between single speed freewheels? (BMX, single speed, "track," etc.)

Will different freewheel thicknesses make much of a difference in how much I have to dish the wheel?

Are "track" freewheels threaded like track cogs or are these intended for the other side of a flip-flop hub? In other words, if I screw one on my 10-speed hub will it only go in reverse?

Is something that is compatible with 1/2 and 3/32" really just 3/32"?

Is there any reason to get a new chain when swapping out gears if the one that's on there is fairly new?

How dangerous is a "suicide hub" fixie, really? Am I going to have problems if I add an English BB lock ring? If I do, do I still need to hose everything down in Lock-tite?
(And why wouldn't you spring for a $3 lockring?)

Sheldon Brown mentioned that some cheap track gears aren't fully threaded. Are there any I should be aware of?

Will using fixed gear put a lot more torque on the crank? Should I consider converting from 1-piece to cotterless if I go this route?

What should I use for a spacer on my axle? I've seen a few builds with what looks like a single anodized spacer, but I haven't been able to find anything like that for sale.