unless the current hub is in bad shape, there's no need to get a new hub to make that bike single speed.

if you have a bike co-op nearby, or some friends with proper tools, you can remove the freewheel (if it's a threaded hub) and simply buy a $20 single-speed freewheel, grease it, and screw it on.

use a chain break tool to shorten the chain you have, maybe lube it up, and you're golden.

make sure you save all the old parts you remove. they can come in handy someday.

on some of those old brake setups with the "turkey levers" it's possible to remove them. they're not useful for braking purposes. if you're handy with a screwdriver, don't be afraid to take it apart and check it out.