i think you'll find maintaining mass and IF is pretty easy. ive been doing 15+ hr fasts 5-7 days a week since april. body comp has improved ... but i think ive actually gained about 5 lbs in the last 2-3 months (without trying to gain mass!) on this schedule.
steve summed up IF and food timing well in another thread:
in my experience - fasted cardio is pretty easy. easier for me than fasted strength or oly sessions. usually, i do fasted cardio in the AM - and don't find that i need any caffiene to get through it. i guess its important to point out my "cardio" is crossfit style metcon's - and rarely over 20 minutes. fasted, intense cardio 30+ minutes has been tough/not possible for me.