Which build are you playing, just to be sure? In the December build, Yamabiko gives you a skill after defeating her, but it isn't coded in yet. In the January build, she just doesn't give you a skill at all, which is intentional, as the only monster skill coded in is the slime wall. As for the items, assuming you mean the ones in the second screen and not the first one, some are key items, so you can't equip them because they're not meant to be equipped, but rather used elsewhere. If you are playing the December build and mean the first screen, same idea as Yamabiko's skill. The framework is there, but is not implemented.
Are you using the settings on the top of the game window or the settings in the game itself? The former doesn't work at all, but the latter should work just fine.
It does, but you'd need to either be able to read Japanese or mess around in the menus to know. The first button is New Game, the second is Load Game (as in functionality, I have 0 idea if they actually say that).
Once again assuming you're on the January build, go fight Mashira.
