Questions Regarding a Character Build

I am looking into making a Beckoner (Chanter subclass) / something else. I am currently considering Druid, Priest, or Paladin as the other class, and I am looking to have the race be Nature Godlike.

For Druid, does the Lifegiver subclass prevent Chanter's summoning invocations in its ban? Also, how bad is the drop in Power Level after shifting (and is it after shfiting until end of fight or just while shifted)?

For Priest, does the Eothas subclass get Returning Storm or Relentless Storm?

For Paladin, what subclass would be best for supporting summoned monsters?

In general, what class (presumably from these 3, but open to suggestions) provides the best in terms of support and healing to summons (and party members)?

Finally, which of the above classes might have trouble triggering manually the Nature Godlike Wellspring of Life ability?

Any insight on this matter would be greatly appreciated.

Thanks!