trail, since you are just starting out and (sort of) knowing your condition, I would take your resistance exercise really easy at the beginning. Your supporting muscles are going to be very important because of your structure (please don't take offense to that it is not meant that way). Things like your hips, shoulders, knees and wrists are going to be very important.
If you are going to be starting out I would begin with fairly light weight, something you can lift for 15-20 repetitions at a perceived exertion of about 7 out of 10 to start with - enough to feel it, but not to the point you are straining yourself. Make all of your movements slow and controlled - at least 2 seconds to lift and lower anything.
Remember to try to make your movements functional as well - lifting, pushing, pulling, and even bending and squatting once you can handle it. A good way to start with the lower body is to do chair sits - just get up and down from a chair slowly and think about using your lower body to push yourself up (if you can handle it at this point).
Good to hear you are starting some resistance work - it will help. Remember it isn't about how much you lift, it is doing it properly to establish a solid base that counts at the start.
How did your weigh in go the other day?