Advice for a newbie on how not to overdo it?

Yes, doing 30DS twice a day would be too much, your muscles need to rest. Yes, doing two workouts a day is probably too much for someone who hasn't done structured exercise in years. You're still in the beginning stages of your diet and exercise program and you risk burning out or injuring yourself if you try to do too much too soon.

Keep going with your eating plan and exercise once per day. Give your body a chance to adjust to all the changes you are making, and give yourself a chance to make exercising and your new diet into a habit. You will still lose weight this way, the only difference is that you're more likely to stick with the plan because it will be sustainable. You can always add in more exercise later as you lose weight and become stronger, or if you decide that you are really enjoying improving your fitness and want to work towards a goal like running a 5k or doing a pull-up.

Welcome! For me, I think to myself, what kind of exercise can I do which I can realistically continue? I think if you approach your exercise with this kind of mindset, you'll unveil what worksfor you, for the long term. In the beginning your double exercise regime might work, but just think, can you do it, long term? Good luck. If you like, Add me as a friend and we can support each other. Positivityis needed and we can help each other.

Take it easy when you hit Level 2. Like you, I had not done any structured exercise in years and wound up injuring my ankle during Level 2. I later read up on it, and injuries are quite common for newbies during that level. Listen to your body, and if you find your joints are becoming sore take a break.