Hi Charity! Sounds like you're got it all pretty much right.
1. A good place to start is 3 sets of 12 - 15 reps. Pick a weight that gets challenging (if not impossible) somewhere between 12 - 15 reps. If you can't make it to 12, you know to drop the weight next set. If you get to 15 and keep going, you know to go heavier next time.
2. Yes, start with your large muscles first. Your largest muscles are in your legs, so do legs, then back, chest, shoulders, bi's and tri's. Abs are good finishers.
3. If you're doing a full body workout (all the muscle groups listed above) each time, you need to be sure to skip a day between workouts for recovery. Three days a week works well, like M - W - F or T - Th - Sat. As you progress, you may want to split up your workouts to focus more on specific muscle groups. A good split when you're ready to move on from full body workouts is to alternate upper and lower body workouts.
There's tons of info in the 'sticky' threads here and on the site Susan posted, so read away and don't be afraid to ask questions.
And congratulations on your fabulous weight loss!