The most important thing is chain line. That is the first thing to address. Get the spacers and make sure it is correct before you ride it. Like the last post said. If you don't have sloping drop outs then you will need a chain tensioner of some sort to keep the chain in tension. You can use the Deraileur that is on the bike by locking it with the limiting screws so that it can't move in or out. That would be the cheapest but least pleasing looking option. If the drop outs are mostly horizontal then just adjust the chain tension by moving the wheel back in the drop out to adjust chain tension. Remember not to tight, should have about 1/2 inch or less of vertical play at the middle of the span between front and back ring. Fixed gear is another matter and has it's own set of requirements as to hubs. Don't worry about painting until you find out if you like it. That should be the last thing you do. Good luck.

fixedgearhead