Ryo

I'm okay if the new mount is of "the same kind" as the original one, i.e from white pegasi to dark pegasi or standard wyvern to whatever Camilla's riding. But other than that it wouldn't make any sense.

16 (including Corrin) according to FE Wikia.

Oh, I totally forgot to check that out. Thanks.

What would happen if we killed Takumi in Birthright Chapter 10 (Ninja Village)? Would he just retreat? Are we able to use him afterwards?

I heard that there's a lobster reference in one of Ryoma's localized support convos? Is that true?

Both Benoit and Zero are fine if you really want to use them.

Or you can simply unlock the chapters after you've beaten the game, in which case the grinding doesn't matter anymore.

All save files share the same amount of points (kinda like renown in Awakening), but you need to update your data first.

That is definitely strange, that doesn't happen to me even after I updated my data. Otherwise I would have thousands of points right now. When people visit your castle and do stuffs (like buying weapons, doing battles etc.) the game would keep a log of their activities. I know those were their actions and not mine because at the time I'd never bought anything from others' MC nor had I done any MC battles. Though I only know that battling people (which I did recently) would also net you some battle points, however I don't remember if that also increases visit points or not.

Doesn't that give them visitor points? I have been doing that to people all the time and I'm pretty sure I don't get any extra points for it. However, I do gain points when people visit my facilities or do stuffs.

No, only when they're visiting yours.

Sadly, no for this too.

Actually Kamui won't gain much EXP in chapters 4 and 5 for being quite overleveled (and in C4 Kamui will spend most of the chapter going around activating those DV because Ryouma won't do that for you, even though his sisters' lives are on the line), so you shouldn't use Kamui too much anyways (other than maybe boss kills). You'll be sacrificing EXP from Suzukaze instead. Even so, in chapter 5, Rinka will have a very hard time in higher difficulties because she has WTD against everything in that chapter; her Def is irrelevant because the main threats there are mages... and mage reinforcements. You can try to give her the boss kill though.

The first part of the two Invisible History DLCs. Note that it's male only.