Those are the ones that you can choose from. The reason The Black Knight isn't there, is because you DO use him in the story, but you can't technically recruit him. Dheginsea, Sephiran, and Ashera are not listed, because they are too over powered, and wouldn't be much of a challenge. The idea is to be able to recruit bosses, while still having some challenge. Zelgius is added, because he's never legitimately used. You recruit the bosses in the chapter you get them, and Zelgius is available at the base of Endgame. All bosses will have a second, and third tier for those who don't have it normally. However, aside from Izuka, Hetzel, Lekain, Levail, and Zelgius, each boss will be given the choice to have their mastery skill. The reason it's a choice, is because some people could think of much better skills for that unit, rather than using their mastery skill. Regardless of how many bosses you recruit, each one is given an "Occult" scroll at base. [In other words, say you recruited Jarod, on Micaiah's team. On Part 3, Chapter 6 [The chapter you use the Dawn Brigade again, when you fight Lethe & Mordecai] Jarod will be in the base, and in his inventory, will be an Occult Scroll. Feel free to explain why you choose which boss you recruit, if you feel like it. Each boss you recruited will still be on the "choosing" screen after Part 3-Endgame, so you don't have to worry about them getting removed. For units like Mages, or Knights, feel free to CHOOSE what weapon they get upon promotion -- for example, if you recruit Veyona, you can choose to give him Fire, Thunder, and Wind [since all 3 are together when picking them] on promotion. Units that are on horseback, have any choice of the 4 main weapons -- Swords, Axes, Bows, and Lances.
As for me, I would recruit Sergei, Catalena, and Jarod. The reason being, I don't like killing Jarod, and think he should've been recruited. [Jarod vs Numida, all the way.] He just seems to be a badass character, that has the potential to be a Male Nephenee, in my opinion. Sergei's character looks fantastic, and I kind of like knights. On promotion, I would give him axes. Finally, Catalena is just...awesome. She's beautiful, she has a much better looking battle animation than the other Pegasus Knights / Falcon/Seraph Knights, and her conversations with our heroes is quite funny. How about the rest of you?