How do I know if I have enough AP and vitality to recruit multiple creatures at once?

[Ungod]

I want to get 6 remains, but I'm afraid I'll be stuck here and maybe not even get all 6, but 4 or 5!

[Demonic God]

The recruitment cost scales linearly with your creature count, starting from 0 (which defaults to 1 - nothing is free!). This means the third creature costs 2x of the base price, 4th costs 3x, etc.

To determine if you can afford something, budgeting is a valuable skill. Having someone to bail you out in case you screwed up also works.