The plane would be better off with the HS-55's. It is already setup for that size, and they are lighter. If you do not have them, or don't want to spend extra money, you can use the 3101's. I used them when the plane called for micro such as the HS-55's. They are just a little heavier. But then you have to deal with enlarging the holes in the plane and worry about cutting things. Easier just to get the servos that it is designed for.

Yes you could use a LiPo, as long as that ESC has a programable or LiPo low voltage autocutoff, which the stock one probably does not. You could only use a 2S 7.4 volt LiPo with the stock motor. A 3S 11.1 volt LiPo will turn that stock motor into a smokeshow in about 15 seconds.

My suggestion would be to just go brushless. Don't waste your money on another brushed 400 motor. You can get an outrunner that will require little work to get it to mount. You will also need a brushless ESC, which are more geared for LiPo's. All around just a better, more powerful setup.