Hey there glad to hear you enjoy it!
Not knowing your full fitness level, I would say that three days a week is enough for at least the first month or two. Gage how sore you are after the first couple of weeks and if you feel like you can through another day in, I would highly recommend it. Most gyms will recommend an ultimate goal of 3 days on, 1 off, 2 on, but this ends up being unrealistic for a lot of people. That schedule is based on ideal sleep, nutrition, etc. That being said, that's the schedule that I follow now. I would say if you aren't experiencing any really bad muscle soreness after trying MWF, through in Tuesday, and then on Saturday maybe do some interval training like sprints on your own.
~All luck is earned in the end.~