I have no experience with this, but I do know that maintaining bone density is not one of the benefits of cycling, because it is not weight bearing. The running and weight training will help you with it, though. You should aim for 2-4 rest days between weight training sessions, so twice a week is better than once (assuming you hit all the major muscle groups in each workout; if you only focus on one area, you would want to rest a couple of days before working that muscle group again, but you could work out different muscle groups the next day.)

Good luck.