I commented on this in the chapter discussion thread but I think there'll be at least 6 Paladins, and potentially up to 9. The "6" is assuming Lucius doesn't give Lucifero to anyone (he's eaten his hearts, so that's different and probably not something he can give back; dunno about his soul tho), Adramelech isn't purified (he seemed to be on his side) and that there's no way to get Lilimaah's soul (since it was killed by Asta). In this case, the lineup would be: Beelzebub (Lily), Megicula, 6th Layer Devil, 5th Layer Devil, 4th Layer Devil and 3rd Layer Devil. The max of "9" would be assuming none of what I said beforehand happens (adding Lucifero, Adramelech and Lilimaah as souls for the Paladins).
As it's been commented, I also think Damnatio should be one of the Paladins. Another potential candidate for Paladin could be Augustus Kira Clover, the king of the Clover Kingdom. For no particular reason, I just thought it would be fun if he was converted into one lol. If Sister Lily can become one, then he could also. I think it would be fun to give the souls of these devils to characters that haven't been very relevant up until this point, but that have been in the series for a while (Sister Lily and Damnatio fit in this description, as well as Augustus Kira Clover for example). Sekke can be another potential candidate as well.
As for their power, if they're meant to have the full power of the Supreme Devils (but purified in the form of "angelic/sacred") then as strong as them, perhaps even more powerful. We don't know if the host of the devil's soul can also use his/her innate magic. As in, the raw power and innate magic of the devil are added to the raw power and innate magic of the human. I think the main purpose of the Paladins (besides serving as the elite guard of the likely Final Villain) is to showcase the power of the Qliphoth Tree Supreme Devils we didn't see fight, so I expect them to be comparable to the actual devils of the Tree (just that the nature of their power is different).
I said about 9 Paladins, but to be honest, I can perfectly picture more. Nowhere is it said that the Supreme Devils are the only ones that can be used to create the Paladins. High-Ranking Demons like Zagred proved to be pretty powerful in their own right, and there should be many of them scattered across the 7 levels of the Underworld that Lucius has taken control over. The main reason why I think it won't likely happen is because this is already looking like a nonsensical lineup for the protagonists. I cannot picture what Tabata will do to make them stand a chance if what I said is true. Adding even more Devils would straight up make this a nightmare (of course, I can see it as a concept, but Tabata would really be pushing it, making their eventual defeat harder to swallow).
