Is group Muay Thai sessions 3 times per week and private MMA sessions 3 times per week a good combination?
You should have some group MMA sessions also. How you approach and apply some things is slightly different from one person to the next. You are more likely to learn that if you workout with and train with a variety of people. Then you will learn what adjustments to make based on things like they being taller or shorter, faster or not as fast as you, or stronger or not as strong as yourself, etc. Also you can more accurately gauge your progress in comparison to others and also use that as a motivator in training. Always working out with the same person will not give you any of this and I have actually seen a student or one in training become demotivated because they are only taking lessons from an instructor or coach. They have nothing else to compare themselves and their progress to.
It sounds costly, but also like a good training.