Re consequences of nat 1 summonings, I’d suggest leaving it sort of general, so yourself and future GMs can improvise based on type of spirit, circonstances, etc?
If you want to balance it without a confirmation roll, you might give something good on a nat 20?
Hmm not a bad idea. Maybe the GM can make a random roll or depending on the situation. Here maybe I just want to say the spirit manifested, glared at you and then left