Rachel,
I am not an instructor either, but share some of the same goals and feelings you talked about. I am currently certified through Rescue Diver, and here is my recommendation:
As soon as you feel that your skills are up to it, get your AOW and Rescue diver. To me, AOW was a throwaway class. I didn't feel like I learned much more beyond OW, and the short class time and only a few dives didn't really give me more than I already had gotten from OW. Rescue on the other hand was great! I can't tell you how much better I am as a diver and how much more aware of things I am both in and out of the water since taking that class. I would get those classes done, try to get as much of your gear as you can to save on rental fees, and then dive every chance you get. Even if it is getting together with a local dive shop and just tagging along on other peoples c/o dives. I guarantee if the shop thinks they have a chance at teaching you DM and IDC, they will fall all over themselves trying to help you out. Also try to go dive in different places. Don't dive just the one local lake or quarry, and don't just dive in the carribean. Get a wide variety of dive experiences in good and bad conditions so you have a depth of experience to work from. Alot of people with 100 dives are better divers than those with 500 dives because of the type and variety of their dives and the level of attention they pay to what goes on before, during, and after the dive. Somebody who regularly gets all their gear together and plans a dive with his or her buddy is naturally going to have more experience and better planning skills than somebody with twice as many dives who has done all their diving at a full service resort where the staff sets up the gear and sets the dive parameters. Beyond that, nobody can tell you when you are ready, but I do think 100 dives is a good number to shoot for as a target for DM. Beyond that, it will be more important that you are comfortable with your skills and abilities than that you have some set number of dives. Imagine the worst possible scenario you can think of on a group dive (lost divers, bent divers, boat trouble, etc) and then imagine having to be the person in charge of getting it under control and taking care of everybody who needs it. If you aren't ready to be that person, you aren't ready to be an instructor. Good luck with getting rid of your shoes!
AggieDiver