1: no, they have to have an interaction or syndrome applied to them, which at the moment can't be done innately. Something has to apply it, like an on-contact syndrome attached to a body fluid they leak constantly (saliva in their mouth for instance) or a cdi interaction that targets themselves and others of their kind. Once applied the syndrome can take effect normally and the cdi can be set to not target those already affected.
2: No, closest you can get is an immobile creature that looks like a plant most of the time and can't interact with other creatures, and then turns into a different creature once infected as per above. Or fruits that when eaten can grant the consumer the power to summon such an immobile creature.
3: temporarily, not a lot, as long as they don't need to eat or drink.
4: if infected by an interaction as per above that grants the appropriate tags, yes.
5: not a clue. Civ members and pets alike with the [equips] tag and functioning grasp parts will spawn with clothing and wear it until it disintegrates, may try to grab new clothing while intelligent, not sure if they will while not intelligent. Civ members that aren't intelligent on spawn will be treated as pets.
You could instead make them intelligent by default and the interaction removes their intelligence for the majority of the month.
6: if they're historical figures and defiled a temple, theoretically, but not being a valid sapient civ members might prevent them from doing that. An adventurer who is an unintelligent race but can equip/grasp should be able to roll divining dice until they get cursed.