Decisions for a campain setting?

[Nadaka]

d20 modern would be different, different is good. Homebrew system, meh, I see no reason to reinvent the wheel. If you want to establish your own system as a spin-off from d20 like True 20 -- go ahead.

As for Core D&D from a legal, publishing perpective that's not possible. You must use the d20 system or the OGL (ie you can't reprint the Player's Handbook verbatim and currently can't use the Dungeons & Dragons name).

I am aware of the OGL and d20 STL, using "D&D" i wouldn't need to reprint anything, nor would I want to. Though I suppose I could have picked a better term to use, though I do not consider "D20" to be descriptive enough considering the multitude of variants out there.

Consider Grim Tales? It's heavily founded upon D20 modern and can plug in any magic system you can imagine with a little effort.

I have read a few reviews of grim tales... It looks like a decent fit. And it has the advantage of being based on d20 modern (all time favorite game for me). Though to get the high fantasy feel, it looks like I will still have to invent a new magic system.

I'll have to look at Grim Tales further, but it looks like that or d20 modern itself as a base.