A single stronger summon would be still be very useful. Obviously not as powerful as a trio of them, but it could be worth it to resolve the OP affinity + Twincast combo. I think the existing absence of miscast chance should still be there imo - it would suck hard to get an archmage and then have him die off by his own summon, especially now that you only get 1 (Runewyns especially come to mind).
Removing Enraged from Skeletons would make them a bit more viable. I find that currently skeletons are very much "fire and forget" type spells, and only on the off-chance one of them survives somewhere out there do i bother considering them a unit - even when summoned next to an enemy stack they usually run off to find something easier to kill (understandable, since they quickly fall off in strength) but this could let you actually retain a small defensive skeleton force.
Having the Library earlier sounds like a beneficial change. As you said, the Laeran Cord are currently very much a late-game religion (especially given the current absence of spellcasting for their Scribes/Saperes); i find them very comparable to The Between but lacking the mobility that religion offers in the early game. It should definitely require a Library to be built, and be blocked to Doviello (and Clan, by extension).
I was going to comment on Zealots and Firebrands having the same tech + building prequisite, but i just noticed that's shared by a couple of the new religions: Ember Legion, Eternal Cabal, House of Plenty and Ring-Givers (the HoP Curator actually lacks Gallery as a prerequisite, but this has already been mentioned before). HoP Curators & Techtons should probably have Priesthood added as a tech requirement, while i think Zealots & Sextons should be bumped down to only require Philosophy.
Additionally, Techtons and Tinkers also actually cost the same (200, with double speed from Enchantment). I think that rather than lowering Tinkers to have the same cost as other disciples (with a commesurate reduction in work speed), Techtons should be increased to 300 in cost. They're already some of the best disciples/priests in the game due to their worker abilities - the Ring-Givers is such an amazing mid-to-late game religion (i absolutely love their tanks) but they could use a bit of a nerfing tweak.