I do not think so, as far as I understand, it is just there because they have been accepted as a playstation game if it does get the funding they need. Or so I assume at least.
If fig doesn't go through, you wont be charged, so there is nothing to claim.
As far as I know, you only get to see the golden costume that Grave has on the fig page:
They have, but it is on the 100$ tier, see golden grave costume.
If the game is successful enough, there is quite a few other characters to choose from within the Fantasy Strike lore which is featured in Sirlins other games such as Yomi and Codex. But then the game first needs to get funded on fig, and then it needs to be successful after that again. So it will not be in the tiers.
I don't know, but there could be one. There is lore to support it already from previous board games.
Normal health bars are just points too, Fantasy Strike just decides to have fewer points in a healthbar. (Ultimate Marvel vs Capcom 3 has an average of 950 points in their healthbar)
That would be awesome, I would enjoy either Dive or Kick from Divekick. But as with DLC, it needs to get funding for the first 10 characters first, be released as a game, and then be successful to be able to go so far as to have guest characters. I think it would be exciting to see more "complex" characters be redefined in Fantasy Strike, to their "core" mechanics.