As has been said already, a superb first attempt. 1,2 and 4 are absolute belters.

I'd say 4 it may be interesting if the bike were more toward the left of the frame than right. Personally I like to have more space infront, like you've done in #1. When panning, it seems to accenctuate the speed and impression of movement forward. Static, with long exposures, the reverse can be true.
eg 1 Cack cause I clipped the back end, but....
eg2 works for me cause it looks like he was going
too fast (which he was)
But that's just my opinion. Don't know if you agree. It's very subjective this game. Just something to ponder regarding options for composition. Hope you don't mind.