Regarding progression, without spoiling too much, there are ways to get additional powers that have nothing to do with your level. They could build on this based on other decisions you make similar to the original BGs where you would gain additional powers and increased ability scores based on your story progression, choices, and alignment.
Not to spoil much myself, but I can only think of one extra tadpole power you get in the EA.
in the underdark from the mindflayer merchant
If you know of more drop em in a spoiler tag and let me know…
