It's a really good idea to plan out your marriage pairings beforehand and make sure you actively try to cultivate them while playing as you'll only have about 5 chapters to do it (albeit super long chapters that are basically multiple normal FE chapters in length). Gregster's suggestions will do you fine.
Characters who aren't centered around a single quirk, being on NX, having a less important avatar, and revival of the old weapon triangle and trinity of magic as well as durability.
In your opinion is it a good Idea to play thracia776 after you finish the adult generation of holy war, but before the child generation? After all, that's the order these events occur.
I'd really like a lord who isn't "Super awesome hero that everyone loves." I think the whole game would benefit from having less black and white good and evil representations, rather having the main lord do some things that might be questionable to the player.