well, if the project is going to have Open RTP http://easy-rpg.org/wiki/development/sample-game then the story must be set in a medieval time, because making tilesets is more complicated than making any other resource, and having done a Open version of the RTP with tiles corresponding of those of the RTP, it will not take too much time.
The characters used could be wathever, because making character sprites is easier than tiles, but they must remain in context with the setting. Of course the material (in RPG 2000) is not entirely medieval, it’s more like a mix of Dragon Quest and Final Fantasy (more the former than the latter). So any story in any of those two settings could be made.
Well that’s my 2 cents.
Historia Makeros was a good story, but had many authors that I don’t think it’s a good idea to use it.