All the classes expect for Nightblades, Assassins and Vanguard receive some kind of bonus or ability between 3-5 level. Is this intended? Fighters/explorers inspire moral, Clerics, Spellswords and Magic-Users can begin some spell research, Bard start learning spells and Theives can Read Languages. So clearly some of the other demi-human classes and campaign specific ones have them, which makes me think this might be an over site.
The Vanguard can easily pick up the morale bonus. Assassins and Nightblades could grab Read Languauges like Theives, but that doesn’t seem like a great fit expect for stressing that they can also operate as spies and decipher codes. Perhaps something like being able to brew poisons like an alchemist?
I’m not sure that they need an additional buff… Both classes get continuous bonuses to thief skills, backstab, spells, etc…
If it was a buff, I don’t think I’d make it Poison, as that’s something that’s directly beneficial to the Assassin/Nightblade in combat. The 5th level bonuses are directed at resource gathering, fellowship, etc.
Well the Spellsword is getting spells and fighter damage bonus and they still receive 5th level spell research. I don’t know how those bonuses factor into custom class creation, but other classes built or mixing similarly are still getting one of their parent classes ones.