Excellent suggestions above. I would add the following.
0. Completely ignore what bells other are using. Completely ignore what bell they started with too. You do you.
1. Get some instruction in the swing, snatch, press and TGU.
2. Get the 16k bell. You'll probably master the two hand swing with it very quickly. Then start working in one hand swings. Once these are easy, start working in the snatch once a week. While your doing this with your 16kb, start working the TGU with the 8k.
3. Also, start working on pressing the 16k. Once this becomes too easy, transition to the bottoms-up press. Work the BU press until it is mastered. Between the one arm swings/snatches and the BU press your grip will be much improved, even with the 16k bell.
4. Once you're close to owning one arm swings, snatches and bottoms-up presses with the 16k and TGUs with either bell, buy your 24k. Keep your 16k and 8k bells. Never sell a KB.
5. Repeat the above with the 24k for ballistics and presses, the 16k for TGU.
I'd add goblet squats and eventually KB front squats with the bells at hand to round out the strength goals.
I personally think that you can get a lot of mileage out of a 16k. Yes two handed swings will become easy fairly quickly but working up to snatches, BU presses and the TGU will take you while and build the strength and conditioning needed to safely tackle the 24k. Fix your diet and the snatches will help you burn off the fat.
You already hurt your back once. You get weak and flabby very fast when you can't train at all. Check your ego at the door, grab a 16k and own that sucker.
Building muscle takes time. Enjoy the journey.