Yes, the Rollei QAL-50 quick-release plate is compatible with it, as the tripod head is Arca-Swiss compatible. The plate also features a standardized 1/4" thread for cameras.
I think so. Maximum load capacity 8kg. The tripod is very, very sturdily built and makes a very solid impression on me. However, I have to say that I use the tripod for a projector.
The centre column consists of two parts that are connected with a thread. If you unscrew this tube and leave out the lower part, the remaining upper part (where you screw the camera or tripod head on) is exactly flush with the tripod part with the leg rests. In the lowest possible position where the legs are almost horizontal but still engage, you are then only 21mm above the ground.