1. Can they be F2P?
2. Is there a minimum level?
3. Do they have to play at least through the starting area?
4. Any other F2P (assuming 1 is 'Yes') restrictions (using the chests in a kinship house; decorating; etc)?
2. Not really, they just have to have left the Intro (i.e. they need the passive skill Novice).
4. No restrictions, they can do anything that their rank (recruit, member, officer) has permission to do.