You don't need to use any special shakes or weird meds. You are doing a great job already! Good work!
Your arms are going to be flabby with the kind of weight loss that you're doing. It will take a bit of time for the skin to shrink down a bit, and it will probably be looser than you're used to because you're losing so much fat. I don't know how much weight you're hoping to lose, but it sounds like you're on your way to a big goal. Keep going!
You should start some weight lifting as you are comfortable. Weight bearing excercise is important for bone strength too. Most gyms have a free program where a trainer will show you around the weight room and how to use the machines. (I attended the YMCA, and they actually have three free sessions with a personal trainer.) There are also great books that you can pick up at the library. One that I used was "The Body Sculpting Bible for Women", although I ignored all of the dietary suggestions. They have great pictures and descriptions of each of the exercises, as well as a routine for you to follow. It's a great way to learn new exercises.
If you have not ever used weights before, it's a very good idea to save up and spend money on a couple of sessions with a trainer. They can show you the correct form for all of your exercises. This is important for two reasons: 1, to prevent injury, and 2, for maximum results from your effort.
As for vitamins, my doctors (I've just been through a few) always suggest that I take a daily supplement -- just something like OneADay or whatever generic there is. You can ask your pharmacist for suggestions too.
Congratulations on your great choices, L.! It sounds like you're doing a terrific job.
PS -- I think that the best strength exercises to start with is pushups. Start from your knees and work up from there. The library probably also has workout videos, although I haven't checked.