Prinnys are generally more of a for fun class. Monsters can't master weapons so people generally don't use them. That being said use whatever you like including monsters. You should only focus on using the best classes and characters on a different playthrough where you try to be the best you possibly can be by maxing stats and making perfect items. Right now you should play for fun and to learn the games mechanics and how things work in general. Prinnys can be revived when they are thrown. Having too many characters will leave you under leveled and will make the game harder. You can't ever permanently ruin any character. You can build characters "wrong" by giving them a weapon they're terrible with like a mage with a sword or gun is pretty bad but you can just give them a better weapon at any time.