[@Bishop]
I will be using a battle system, since PvP devolves into a bit of a freeform mess without at least some structure and means by which players can actually kill one another. 

[@KoL]
I won't be incorporating my own headcanon, if that's what you mean. Everything will be staying along the lines of the Type-Moon world. 
As for canon servants, you're definitely allowed to app them, but there will be some restrictions. For instance, some will be banned because of balancing (eg, Gilgamesh), and some because we don't have their full information (eg, a lot of the Strange Fake, Fragments, and Grand Order cast).