Dorter Trade City is generally reckoned to be the first serious battle in the game, yeah. Back when I was new to FFT, I lost a character and continued anyway just to be through with it.
Gil rewards are based on enemy level, IIRC, but War Trophies (which sometimes include extra Gil) are set for every battle.
Dycedarg and Zalbag are Ramza's half-brothers. Alma is Ramza's full sister. And yes, Teta is Delita's sister.
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I don't like this duchy. Now, it's an adventurer.