With regards to the Zealot not having enough access to 'religious' skills, please remember this paragraph from the PHB about customising a background:
Customizing a Background
You might want to tweak some of the features of a background so it better fits your character or the campaign setting...
I've just finished a 'Session 0' where some level 12 PCs escorted an Ambassador from Waterdeep to the Storm Kings Court after the Ordniing has been shattered (honestly, that's a pretty big deal and would have been noticed by clerics of other faiths!).
While they were there met the giant lords...
I'm happy to run this in parallel; share the encounters with me and I will run them with one of my players and return the results. That will give an additional data point and feedback.
Which is all fine if you want to DM a group of murder hobos. But, given that the NPC Archmage offered you a mountain filled with magic items and enough dragon-shaped experience bundles to level at least once, all for the very low cost of half a day's work, I think you've missed the point of this...
Happy to help out where I can. To make life simple, you could use the level 13 PCs that Celtavian created, with minor personality adjustments so they are actually interested in things like the fate of the universe.
A lot of back and forth to test whether the 6-8 encounter adventuring day is working as intended.
The fluff is nice - but can't we just assume that you've provided a hook that is hook-y enough to get 5 level 13 characters to do a thing inside 5 hours?
Given the conceit that in any campaign a...
How are you thinking of managing the backgrounds? From what I understand, the backgrounds/themes give some interesting powers in 4e. Are they necessary/desirable for a 5e port?
This is really cool - I'm happy to update with extra subclasses (like Totem Warrior). Do these get saved for everyone to share or just the individual user?
I'd say so - I'm planning on ruling that way in my game. And you'd be able to grapple so long as you had the other hand free.
I'd treat the the shield as an improvised club for damage.