lots of good stuff your getting here.

go to as many bike shops as possible and feel them out. your not just buying a bike from that shop, you should be buying service and some level of continued support. getting an average on advice between shops will help determine if somebody is more interested in selling you the right bike or just selling a bike. Sometimes they want to move what they have on the floor more than anything else. not always, but it can happen.

The thing with a used bike is this. If you know what you are looking for and at, then its fine. If not, then you can get burned.

Also, try out as many saddle options as possible, both when you buy and possibly later. as your miles climb you may find that a gell unit that felt so nice at ten miles is moving around to much and chaffing, as well as soaking up energy on your leg movement. Drop bars look really uncomfortable but they are nice for a long ride. if you get a flat bar bar ends can really help.