I agree, you definitely want to shop in Monastiraki! There are individual stores, but you should also visit the flea market. This is one of the most entertaining things to do in Athens because you can pretty much find anything at the flea market.
I'm in the holy spirit but pretty sad that we in Athens can't leave the house to attend church services. I've only been living here for a little while so I haven't gotten the chance to visit many of the churches. What are your favorites?