Love the WR250... Hope to eventually have one, along with a street, once insurance lightens up a bit.
Do you have any 2 wheel experience? I rode dirt my whole life (2, 3 and 4 wheels; along with skidoos in the winter) growing up and started Street last year (at 18 years old) and it is completely different.
What 3 wheeler do you have? I had Honda Big Reds.
I'm not sure writing your M1 now is worth it. Drivetest centers are stopping motorcycle road tests due to winter months coming on, and courses may be doing the same thing. I'd suggest writing it in february or march and booking the earliest training course (should be sometime mid-late march) so you can get your M2 asap.
Unless you can find a course and register for it this year. RTI (rider training institute) runs until November 10th I believe. I think learning curves still has a few more courses (not sure about space available, you'd have to check that yourself.) So look around for a course and register for it before writing your M1, because if you can't get into one your M1 will expire (after 90 days) before next season starts.