1 - From what i understand, damage wise crossbows are better vs armored enemies, while bows are faster and better for unarmored enemies. But does that remain true if you add a Knight with weapons that have armor reducing capabilities ?
2 - Does the herbalist use both bandage and healing tonic (the one that requires hearth essence) on the same hearthling and on the same situation/moment? Or is it pointless to have both at the same time?
Yes, your understanding is correct. As for the question, the Knight’s debuff, which is an armor reduction effect, functions for all attackers (so any other lings attacking will also benefit from it) while the archer has an armor penetration effect, which only affects their own attacks and abilities. These are cumulative, so the archer will actually penetrate even more of the already reduced armor (consequently having even higher damage), so yes, Knights and Archers with Crossbow are quite efficient and do not counteract each other.
All of these: Small Healing Tonic, Coarse Bandage, Light Bandage, Heavy Bandage and the Hearthbud Small Healing Tonic are basically the same type of item, a “healing item”, and the only difference between them is the amount of health healed.
A herbalist will pick up any healing item without any other thinking (so usually the closest) and will apply to a wounded character. That means that it is possible that they’ll use something that heals a lot more than it is needed, or also that they’ll use something that doesn’t heal enough even though you have better. So it’s advisable to keep only the best ones, if you can.
The healing system is currently being reviewed by the ACE team, however, exactly for being very simple (and relatively useless once you get a cleric). We’re looking into, among other things, improving this logic so the herbalists will choose better what to use.