I am more than happy to be corrected by others with more knowledge and experience!
I noticed during the video that your forehand is your strongest shot - yet, it's the shot where you seem least ready to play the next ball. If you look at the way you play your attacking forehand, there's a lot of swing backwards before you then play your shot (a little like an old skool loop) - you might find it beneficial, especially when you are close to the table to shorten the backswing on your forehand. It should reduce errors but also you'll find it much easier and quicker to get back into the ready position for your next shot. Also, it takes less effort, which means you can do more of them without tiring so quickly.
Finally, work on the basis that your opponent is going to get every ball back, this way you play each shot and be ready for the next - don't assume you've hit a winner.
For your backhand - I was taught (by a chinese coach) to play the shot like you are throwing a 'frisbie' - multi-ball is the best way to start this - just get the technique right and get yourself used to playing the shot - then get someone to feed you underspin and keep going, then work through to mixing underspin with topspin.
Hope that helps.