Removing Radiator

I want to remove a radiator and cap the pipes. The pipes have been painted.

1) What's the best way to removed the paint without damaging the threads?

2) Should I use teflon tape or pipe dope or nothing on the caps?

When you remove the radiator, won't that expose some threads? There may be a union on the pipe, but just remove that, too, then put on a cap. If you don't use either tape or pipe dope, that connection will leak. You can use both,too. A wire brush should work to clean up the threads, if required, or, if you have one, you could run a threading die over it.