Jenos is very flexible and can fill in many roles (except frontline) with any loadout. Try to find his play style and adapt accordingly.flanking? Group up. Damage? Flank him in a group. Healer? Cauterise.
Chronos. There is rarely a reason to get anything else for Jenos except Chronos if you're intending to heal with him. If you find yourself being hard-countered get Chronos II then buy another item to properly defend yourself.