Hello! I think it's wonderful you're considering adding strength training to your routine.
1. Water aerobics: Do you find this workout challenging? If you do, then I think it's great. Not all water aerobics classes are created equal. I tried one that was just awful and not nearly enough. But they're supposed to be really good, and maybe yours is. One hour four times a week is awesome if this is a challenging workout.
2. Free weights: I'm not sure what to tell you about your back. You should probably check with a physician and/or a personal trainer. They will likely have experience with this. I do some of my work standing, some sitting, some laying down, but I have no back issues. I suggest listening to your body and see what feels best.
3. As for a schedule, your body needs a couple days of rest. I give mine a full seven. So on Tuesdays I tend to work lower body, Thursdays I work upper body and Saturdays I work whole body in a class. There are many ways to break it all down, as long as you are giving your muscles sufficient time to rest.
4. I think lunges and squats are awesome and I definitely think there needs to be a day or two in between doing them. I shred my legs (in an awesome way) by going up and down steps for 3:00, doing 20 squats, then 3:00 of wall sits, repeating this sequence for 3 sets. I also do squats with overhead presses, lunges with lat. raises, and squats with a military press. I like working my legs best.
Long term goal: To still be calorie counting 11/9/2010
mini goals: ~211-10% lost;12/24/09 ~203 class I obesity 1/28/10; ~199 Onederland/15% 2/19/10; ~188-20%; ~185 half way 5/14/10; 179-bye 180's 6/12/10; ~174 overweight 7/3/2010;169-bye 170's 8/13/10;~164-30% 10/23/2010159-bye 160's~11/1/10; 153-35%~12/23/10; 149-bye 150's~2/11/11; 145 normal~2/14/2011; ~141-40%; 139-bye 140's ~135 GOAL! (129-45%; 117.5-50%)
My "goal" story: http://www.3fatchicks.com/forum/goal...goal-post.html