Maul is a bit tricky in terms of force mastery, as it never seemed like he reached a high level of precision, power definitely, but he was always more rage-fueled and the "lash out" type than compared to say Dooku. Thus...
Raw Power: N/A (Baras level?)
Knowledge: No idea TBH; I'd assume not much though considering the limited abilities he showcases and it's fairly clear the saber is more Maul's MO.
Mastery: < Baras
Dooku I have as moderately below Nox as of Act 3 at full amp. Enough for Nox to win a Force only confrontation. Thus....
Raw Power: > Thanaton
Knowledge: < Thanaton
Mastery: ~ Thanaton
Vader is somewhere between the protags and Revan. With Revan being > Vader IMO purely in force capabilities.
Raw Power (realized): < Revan (potential) > All force-users obviously
Knowledge: < Revan
Mastery: < Revan
Number of techniques isn't the only indication of mastery, especially in canon where most characters are pretty much TK/TP/Lightning and that's about it.
An example I'd cite is a dark side novice in the form of Quinlan Vos conjuring a small storm of Lightning around an enemy he was choking based on raw instinct. There's varying degrees of mastery in every realm of the Force.