[Advanced Player's Guide] Beastmaster and Diabolist PrC

[Waldham]

Hello,
for the diabolist, the imp is an animal companion, not a familiar.
is it possible to have several imp companions with the Beaster Master (Advanced Player's guide) and the Diabolist PrCs ?

With the feat boon companion, does the effective level druid improve at the ranger level ?

Thanks for your future help.

[Dragonborn3]

Diabolic Ranger with a small army of imps...

Oh, and *bump*.