The fact that you are trying to change, how you do things, to do them better is great. For someone training himself based on what the internet tells him... good progress.
First off I want to reiterate, get a trainer/coach/sensei... to learn from. Thats the best and quickest way to learn. And if you respond half as well to a real instructor as you did to us folks on the net... your instructor will love teaching you and you will progress.
The hands stayed up more, definite positive there. Yes, you have to condition yourself to do it and they do get heavy, its not just a saying. However, when you kick, you are dropping your hands. Watch the kicks you do in the beginning (after you went through the steps of the kick), watch your left hand. It starts at your chin, then you start to swing it down, when it gets to your hip almost, you start stepping into your kick. With that kind of telegraph, if I am in range for your kick... I will step in with a straight right as your kicking foot leaves the ground. Watch how much time there is between you left hand dropping and the kick coming around to the bag. Fun, time one the straight punches you show later in the video, and see if those punches would have beat your kick, if you start the punch when your left hand drops. (the guy telling you to drop a hand when kicking, was talking about the other hand: right kick - right hand. I prefer to keep both hands up, I will trade any small increase in power it may provide, to keep my guard up while kicking... but thats me... he will probably disagree)
Also, don't switch stance so much... or at all for now. Work one side, finish your combo then step away if you want to try the other side. If you switch stance like that in the middle of the combo or anywhere where he can reach you, you will take a seat when he hits you mid switch.
Concentrate more on the footwork. Your punch starts from the feet. If your feet are not right, your punch will be slower and have way less power.
Keep up the work! And get a trainer!