I guess the first thing to do would be to take a practical look of what you can and can't do safely, long term. Take into account knees and feet if you're thinking of any kind of roadwork or rope jumping, your back if it's core strength or overall strength.
The biggest consideration is time. Endurance work takes time, not just in the "gotta put the time in", but in the practical sense on a clock. If you're working toward a marathon you have to put in the hours. If you were working on your core, you could add a furious twenty minutes to what you already do and be fine. Adding endurance to what you already do....can take up a lot of minutes
I think the biggest mistake any of us make when embarking on new training, is doing too much too soon. Of the two you mentioned in your original post, Insanity would be the far more intense. Just be careful, bro. And have fun.