Tactical RPGs have both styles: top down and the diagonal. The older Fire Emblem games are top down which is what I am doing right now, and then there is Final Fantasy Tactics which is diagonal. All I would is just the matching tileset to go with the rest of the Mega Fantasy recourses, then I would be all set to completely change the resources. I am using RPG Maker FES DLC right now, and there is less than 40 monster character sprites. So, your Mega Fantasy monster character sprites would add a lot more monsters type units.
Fire Emblem! I see, it's definitely a top-down view. In that case, the tileset materials I'm planning to create in the future might be useful! To be honest, I think it will still be a while before I start working on tileset production (probably around six months from now?), but I'd appreciate it if you could wait patiently.