I need to be cardiovascularly fit so I can last awhile and keep the fighting up so I need to know when to do this cardio since I wanna gain size and strength to. My split is upper/lower monday, wednesday, friday, saturday. I don't want to lose any LBM. I am very flexible as is but I would like to know where to stick in stretching, I would do static stretching since I am familiar with this from martial arts and would rather do it after cardio if it's enough.
You probably can't bring everything up at the same time. Honestly, I would probably drop the resistance training down to two times a week for the time being. This will allow you to keep your mass and strength at the same level and really bring up your conditioning in the meantime. Once your conditioning gets up to the level you want it to be, then you can transition back to resistance training three days each week, and maybe four if you really wanted to put emphasis back on size/strength.
Do some static stretching at the end of your workouts a few days each week. I like to stretch almost daily, but if you feel that you are flexible enough and just want to maintain that level, then a few days a week is sufficient.