Do not worry too much about over training......
Think about all the greatest mma fighters....they train around 6 hours a day!!!!!!!!
Lifting weights 4 days a week for 45 minutes and training on the MMA mat for 90-120 minutes 5 days a week will not lead to over training.....it will lead to becoming a total bad ass.
Are you really telling me the only thing holding you back is the Fear of over training?
IF that is the case I think you picked the wrong sport. Dont be scared of overtraining because there is no such thing. Now go out there and train and chase your dreams and goals!!!!!