I woul not say Equestria is based off of America due to the fact that the map we currently have of it does not look like America.
Check again - and this time use your imagination. If can't, then take both map of the USA and Equestria, and start checking - where is Baltimare, Fillydelphia, Manehattan and compare with Baltimore, Philadelphia and New York localization. Then Vanhoover/Vancouver, next would be Las Pegasus/Las Vegas, Neighagra Falls/Niagara Falls, Haysead Swamps/Florida, Dodge City/Dallas...
Of course terrain is harder to compare (Badlands where Gulf of Mexico should be, mountains, etc...). That's what would need some compromise - or more work to do with the map.
Also I believe Equestria may be multiple islands due to there being a town named Trottingham.
IIRC, there was told that this map isn't finished, so Trottingham still can be somewhere in here.
I think it should start with three separate countries like in the hearth warming eve episode, the pegasi, earth pony and unicorns. Also Equestria should probably be an empire level title you can make only if you hold all three of the kingdom titles of the three original pony kingdoms.
Yeap, that's what I was thinking about
Also I think ponies should gain a trait while married to a human that greatly decreases their fertiality due to the species boundries. I know really there should be no chance of children but I can't help but feel that is a little boring and for fun sakes perhaps should be overlooked slightly.
I don't think there should be human... We should really have this mod a "total conversion" one. So only Ponies, Griffons, Zebras, Buffaloes, etc. But you're somewhat right about infertile marriages, i.e. between Pony and Griffon, or Buffalo (Zebra might be "compatible" with, though ).