Absolutely new to actually working on bicycles, so bear with me here...

I'm building up a fixed gear out of an old Norco bike I found on Kijiji for cheap. I've pretty much figured out all the parts that I need, except for the crank...

It has a "swaged crank" if I'm correct, it looks similar to this:


The outer chainring on this crank is the "main" one, and the smaller chainring bolts onto it. What should I do here if I want to make this into a fixed gear? (The outer chainring is about 53-57 teeth, I can't remember my exact count!) Is there any way to replace a swaged chainring, from what I can find it seems that you can't.

If not, what sort of parts do I need to be looking for? Do I need to replace the bottom axle (not sure if that's the right term...), or are cranks fairly interchangeable?

If I am replacing the crankset, what would be a good gear ratio to "start out" with. I'm looking to use this thing for putzing around the city and getting into road biking a bit (I just have an old mountain bike now that I use to go to/from places around the city).

Thanks!