D&D 5E Channel Nature Druid

Trying to actively homebrew an appropriate Druid for 5th Edition for use with the Plane Shift: series, and my best answer has been custom druid circles that decide the available class features simultaneously at 2nd level like the Cleric divine domains, but in this case, with a separate selection of circles per plane.

Two questions to help me get started: #1. Channel Divinity comes with one use at 2nd level, and an additional use is granted at 6th level and 18th level, and uses are regained after short AND long rests. If this Channel Nature feature were to behave the same EXCEPT that uses were regained only after LONG rests, at what earlier levels could one additional use each be gained while still being balanced?

#2. What class as written could be capable of summoning/conjuring Zendikar's CR 13 Kraken (type: Monstrosity) without being an absurdly high level?

The cleric and the bard via magic secrets are the only classes that could possibly summon anything CR 13 via planar ally (level 6 spell). The spell as written doesn't apply to monstrosities, but I would be willing to accommodate that if it made sense for the god/patron/etc. to have something like that serving them.

Oh ok, that basically answers my curiosity if canon Planeswalker NPCs HAD to be stat-blocked, or if they could be built as playable characters, but in this case, I'm not so sure Kiora is identifiably Cleric OR Bard, though I can see how either might just barely make some sense. She comes off as primarily Druid, while Bard fits as she seems to be highly Charismatic above all else and DOES share "Cosi stories", and Cleric fits if you look at her as barely holding onto her past as a Cosi Creed merfolk and using divine magic in the name of a god she KNOWS now is fake. Weird Cleric concept.

But additionally, can't choose monstrosities, so it makes better sense as a Legendary Action of an NPC.

Now just need to balance the Druid

Perhaps one example of Channel Nature could be to use something similar to a Bardic Inspiration die to add the result to the CR of available creatures to summon while casting a spell that conjures creatures, and among that druid circle/domain, have a feature that allows certain other creature types under certain cirumstances.

Monstrosity with some sort of "swim speed" or "ocean-dwelling stipulation, and some stipulation allowing Felidar.

NPCs don't need to follow the character creation rules of PCs when determining ability etc. Build them as a monster, handpick some abilities and enjoy.

Also note, you can be a Nature Cleric instead of a Druid - most of the flavour and Channel Divinity comes with.

I know, but the Monster Manual does suggest it as an option, and I'd like there to be not TOO much of a gap between canon planeswalker NPCs and potential PCs. For instance, I'd definitely prefer Nissa to have qualities that match up with her being a Joraga Nation Elf and some features that reflect her being a druid and/or ranger (her origin story had her like a Scout with a bow, and until her BFZ persona took hold, even IN her Origins appearance, she still had Vampire as a favored enemy)

Also, substituting Nature Domain Cleric for Druid just invalidates Druid. My only MAIN problem is Wild Shape is NOT a trademark ability of most MTG druids, Zendikar gives the option of tweaking it to behave like Totem Armor (Wild Shape that doesn't REALLY turn you INTO the animal, but adds stats, some actions, and in this case, Temp HP, that imo should cancel the ability when the Temp HP is depleted. But if I were to treat Nissa/Kiora as a Druid, Totem Armor doesn't apply to them at all either. Nissa calls on plant roots/vines, plant creatures, and what can only be described as Earth Elementals. Kiora does the roots/vines thing and summons sea creatures (krakens/sea serpents/octopuses) with high Cr, if the 'official' stats of the Zendikari kraken is anything to go on.

Even if monster stat blocks are best for these characters, how many Xth (1-20 of course) level PCs (1, 2, 3, or 4) do you think the following would be a fair challenge for?

Nahiri, the Harbinger

Nissa, Sage Animist
Nissa Revane
Nissa, Voice of Zendikar
Nissa (Shadows Over Innistrad)
Nissa, Vital Force

Kiora, the Crashing Wave (Pre-Bident)
Kiora, Master of the Depths

Sorin Markov
Sorin, Lord of Innistrad
Sorin, Grim Nemesis

Tibalt, the Fiend-Blooded

Arlinn Kord
Arlinn, Embraced by the Moon

Vronos

Chandra, Flamecaller
Chandra (Shadows Over Innistrad)
Chandra, Pyrogenius

Dovin Baan

Saheeli Rai

Sarkhan (Zendikar) (Dragon Form)

Well, now that PS:KLD confirmed along with PS:ZEN that Innistrad is so far the only setting that calls for an unusual build for Humans, then most human characters across the multiverse can be built.

Perhaps a Plane Shift: Mirrodin/New Phyrexia would split Humans into tribes for the Auriok, Neurok, Miriok, Vulshok, and Sylvok.