Ay, thank you so much! Glad you like my stuff!
The specifics of recruitment are going to be ironed out with the next major update, but to start I'm planning on having a few different starting units available for each imp. They'll cost gold to hire, but I do like the idea of some units being exclusive to a certain Sin route (like allowing Succubus to influence certain enemy types to defect and become available for hire). I'm planning on a few factions
being available for recruitment after you find them and beat them at their base in order to make a contract with them.
Maximum number of party members is three (including the player imp), though that might change later if I decide that it disrupts the balance
of the combat. Usually you'll only have those party members while adventuring; you'd recruit them just before heading out on your expedition, and they'll be removed if they're defeated or when you return to your base.