The above posts all contain excellent advice, from other photographers with lots of experience, and should be quite helpful to you.

At present, you've got a good basic range of prime lenses. That being said, I would heed the recommendation of going for a faster 35mm. It's a great all-round moderate wide angle, and comes in use in most shooting situations. Also, use your 50mm as much as you can, as stated. If the QL takes FL lenses, stay with that, if you can... your decision. Don't get hung up on acquiring too much gear; you'll truly end up not using most of it. I, too, wouldn't go the zoom route (personal preference).

Also, the above advice for checking KEH,, for used lenses is the best place to start. You can't go wrong with them. I have 3 FD lenses (35/F2, 50/F1.2L, and 100/F2), all purchased from KEH. I get about equal use from each of them, and have no plans to add on.