The 540's are a good pedal but so are the cheaper 520's. I know some are saying go road pedal- but that will also cost you a new shoe and you will have the problem of walking from the bike into the cafe with a pair of shoes that don't like being walked in.

So go SPD as you have the shoes- and go double sided pedals such as the M 520 or 540's.

Now- to get used to them. practice a few times clipping and unclipping while staionary, and get the tension set up low.And Don't forget to ask how to tighten them at the shop either. Then go out and ride. My first ride on SPD's was offroad on a a 100 miler. And I only fell over once.

So kill two birds with one hit. First clipless fall and first 100 miler. You know you want to.