42-16 or 42-17 or comparable is the best all around gearing for this type of bike.

You should be able to find a decent quality crank at a bike shop, or just about anywhere for not too much money. I've set up single speeds just like yours running on the 39 tooth on the inside of your current crank and then making up for that on the cog. I think (if memory serves me correct, you have to go to a 13, or 14 tooth cog to get the gear inches. I don't have my handy dandy chart here at work. It's not as pretty as a single chainring setup, or as cool, but it will get the job done. I saw one of the easiest SS conversions ever this weekend. The person had simply taken off the derailleurs, shortened the chain and ran from the inside chainring to whichever cog lined up in the back. No redishing, no changing out anything. Just stripping off unwanted shifters and derailleurs and voila! Single speed simplicity.

That's a great bike to start out with on a ss/fg conversion. Not a heap at all. Get busy!

Mark