What are the main rudiments one should learn or is it necessary to learn all 40?
ANSWER
Hi, evandam11--
Of course it would be good to learn ALL of them, but you don't have to do it all at once.
Try starting out with the paradiddle, single stroke roll, 5, 7, 9, and 17 stroke rolls, flams, & triplets.
Then when you see how useful these are, you will likely want to learn more.
Best Wishes,
Lynne