I was looking for some FHs that are not on returns and not followed by net approaches (these you do really well).
0.48-0.49 - pause it.
On this one, you are moving back on a deep ball....on a court that doesn't have enough room. I would try and catch this one on the rise.....you are also late on this stroke...the ball is too close to your body and too far back. What you want to do is have a full stretch of the arm when you hit a forehand. If you can't - then you too close to the ball. And of course you want to hit it while not moving back....and "on your toes" as far as timing. You let this ball control you instead of the other way around.
at 3:37 you do exactly what you were supposed to do above.
5:13 - pause it. Keep your back straight. Need to get to the ball? use your knees.
6:18 - good.
As far as your serve. Technically it is a good looking serve. I can't see the toss because of the position of the camera. You need to improve your lower back flexibility. Way too stiff. You should start serve motion in this position: ) and finish in this: ( Arch your back back and then forward as you hit. You bend your knees nicely on first serve, but it looks like you are doing your coach a favor by doing it....I don't see a power traveling from your legs into the shot...maybe because of a where toss the ball, probably thats the reason, can't see clearly on this video. Second serve - bend knees more.
Work on relaxing your arms and shoulders thruout the shots and serve. I generally get a feeling of you being too tense. Relaxed arms lead to more power, control, spin, more energy later in the match.
In your current form, your coach should work on your timing and repetition. You should work on flexibility of legs, lower back and upper body a lot. I think in your current form, your fitness is more important then your tennis. Yeah, you do some mistakes here and there....but it will polish itself out with repetition and proper correction of these mistakes by the coach while doing the repetition.
If you can, go to yoga, or any other class that includes a lot of stretching. After a few month of such class - you will be absolutely amazed by how much your game is progressed. Why? ....because the coach is probably asking you to do these things that i did now, but your current body state just doesn't allow it, limit you. 6'5 is not too tall....I am 6'3 ...and I have seen a very stretchy 6'5s in my life

Level 13 Edberg and counting...