It has come to my conclusion that you need to have at least 4 things to make yourself a Grail War, the land, the ability to connect with Akasha for the wish which is what the greater grail is, the lesser grail so that you can connect to the greater grail (Sakura, Illya, Irisviel.), and of course the knowledge to do all this.
Caster with her great knowledge of all things magic is able to do all but connecting to Akashi, for that she needs someone with the ability to do it for her which I shall also provide. (Or have already provided heh.) Securing the land would be easy enough, once she finds a suitable leyline (Which I shall have Elf help me with, she would then need the Greater Grail and Lesser Grail parts, also as for gathering up enough suitable prana for it well a big bang is just about to happen in the city thanks to Downy's actions and a whole lot of magical energy is about to just go flying everywhere so all she needs to do is just guide it. (Easy enough for her at least.)
A lesser grail is probably the easiest part anyway with her A rank in item creation she can make things like fake immortality potions creating a lesser grail even a homunculus is completely within her capabilities. (What would also be more interesting is the fact that this grail war would work similarly but differently the the 5th war one so that anyone involved in those would understand what's going on but would be unable to hack it unless they themselves had knowledge of Age of God magic.)
Those are my thoughts anyway, also to help even the playing field I figured that when you decide you want t enter you won't be able to pick who gets the Seals I shall decide that with perhaps a bit of help from Elf if I think I may need it. After you get the Seals however you can then vouch for which class you want if there are any duplicate classes then we roll for it. (Keep in mind the loser will get stuff with whatever classes have not been picked.) (Also to enter in the firs place you'll need either an already summoned Servant or a spare character sheet obviously though if you want I don't mind playing the Servant with one of my open spots, however I can't do that for everyone, I of course may even have Caster summon her own Servant, we shall see.)