I would love to use them and I'm confident others would as well. Showing them off here in the forum is fine, but there is no formal license associated, it is not officially sharing the assets, so they would not get used like they would if you submitted them. Assets that are useful for making assets are just as useful as assets for making a game are; both will contribute to the creation of games. :)

OGA-BY is adaptable to CC-BY-SA, so a derivative of all of them could be in a single submission so long as the license was listed as CC-BY-SA and credit was given.

I saw the site did indeed unpublish your submisson due to suspected spam. This particular day of the year tends to provide me with very little time to administrate the site, so I have only recently been able to look into this. The links of the post are all fine, but I had a few questions for you about the content:

• Are any of the characters in the submission the same characters, in name or disposition, as the characters in the original game or manga? I'm guessing all the assets are made from scratch, but there may still be trademark implications if the characters overlap with the game that your fan game is based on.
• Can you indicate where the other artists who created the assets have given permission to release these assets under the CC-BY license? Although you may have comissioned the assets, the original artists still possess the copyright to them unless there is a contract showing they transferred those rights to you as a component of the exchange. Unless that is the case, the other artists still need to be asked permission to share their assets outside the original commission terms/project.

Beautiful!