1. For the Roman nations, you already made the obvious suggestion in the other thread, Broken Empire and Pythium.
2. Again as on your map, except that T'ien Ch'i doesn't belong in Europe, so I'd replace them with Jotunheim. I'd also suggest Arco in Palestine, just so that the Roman nations don't have a monopoly of Astral magic.
3. I'd say yes to conquering sea provinces. If the map has seas, might as well use them
4. I'd prefer that the Roman Nations are strong, but that there are around 6 Barbarian nations. Victory for the Romans is to hold 2 Barbarian capitals (it migh be easy for them to cooperate and rush Ulm), victory for the Barbarians is to sieze either Rome or Byzantium.
5. See 4.
6. Oh, 50%
7. No.
8. If there were 6 Barbarian nations, it would be appropriate for the Roman nations to have 3 castles each.
9. No. Research will be fast enough without any added boost, at least for the Roman nations.
10. Undecided, but with slight preference for national - if someone can come up with an appropriate set of monsters, I wouldn't object.
11. I like the idea that the Roman nations hold more territory and castles but must use human pretenders, while the Barbarians can use anything they want, and are strongly encouraged to use monsters or Titans. It might even be fun to specify the most thematic pretenders - i.e. Jotunheim must use a Son of Neifel, etc.
12. Possibly, depending on balance. It is going to be hard to balance things, but the Roman powers starting with some "ancient artifacts" might be thematic.