I got to recommend against the used bike plan for a starter IF you try to pick one alone. I'd visit a couple of local bike shops and tell them what you are looking for and get fitted for their best suggestion. Whatever you do, don't buy the first bike suggested. It may well be the one you end up with but you need to talk to that second sales person and soak up the knowledge and recommendations from them.

After you've done that and you've researched fit, THEN you might consider looking used.

Or you could do like I did, buy one of everything until you figure out what you like and don't like.