If you have to start slow, how long does it take to work up to more intense exercises? I want to be realistic but I don’t want to be lazy.

Well to be honest, when i started doing pushups I was only doing 20 every morning then with time i went to 30 and 40. It all depends on your body, mood and attitude toward what you are doing. Take your time, look for what whats for you and start as slowly as possible. With time your body will tell you when to add to it, don’t force it, just take your time