Personally I picture Bithynia with Greek elites on top med Trhaikians (as according to all sources they were a Thraikian tribe which migrated from Thrace to Asia minor) and low level units Anatolian+Thraikian mix (dressed like anatolians). This kingdom was never really subjugated, and never really did become hellenistic, but only his kings and nobles would be, and do so by choice.

Galatians... Love/hate affair, as it was them who invited them over, but then fought many wars against them. Your choice as to whether to have them in your army's roster.