Just make him a paladin straight away. Anomen wasn't much of a caster (and he had better Cha than Wis anyway, at least until he was knighted), and the main thing preventig him from being a paladin was his LN alignment, which isn't a problem in 5e. "Melee fighter with some divine casting" is what paladin does, no need to hang-up on a specific class combo from over 20 years and 3 editions ago. For the same reason, you may just make Imoen into Arcane Trickster... the magery didn't really fit her anyway.