If you can get a good start, Shinuyama isn't a bad nation to play. They've got powerful recruit-everywhere mages and some strong troops.
The longbow Dai-Bakemono are very good, just expensive and resource intensive. Once you get a few castles built, you should be able to build enough of them. More castles will also let you build more mages and you can play around with troop buffing and artillery spells.
Some neat national summons too.
If you can last awhile and expand it'll go well. If not, it'll be over quickly and you can move on.
Playing around with nations that interest you is probably a better approach than trying to find the perfect starter nation. If you get slaughtered, try out the nation that beat you.
