Choosing a formation

I'm starting a psyco demon team and I wanted to know which demons out of the ones I have would make the best formation to start off with or, since I'm in the process of levelling them, are there some other ones I should try to trade out for? I have Blue Steel Devil+, Typhoon+, Belphegor+, DCC+, Taroth and Katone

I would stick with 5x A+, rather than bring in an AA. At least not until you have 2 (or ideally 3) AA+ monsters to bring in all at once.

The only demon you really need for your team is Blood Quencher Sekhmet. She has the Increase Party Attack skill, which is beyond useful for an agility team.

Your other 4 As are all good. Typhoon can be upgraded to Shadow Domain Demon, but that is an expensive upgrade. The new Arbitration Demon is also equivalent to Typhoon, just with Covert Down instead of Impulse Down. So if you are willing to spend the EP to get high skill levels on the guild-down monsters, you may enjoy having one of each to swap out as you see fit.