I disagree with your last point. Yeah, you convince him to not blow himself up, but for my Tav it amounted to “we’ll find another way where you don’t die.” He does get pretty power hungry, but a few persuasion checks and he realizes he was backsliding and agrees with you to cut that shit out. He decides to get the crown for Mystra without seeking its power and she agrees to heal him.
There’s redemption there, you just have to push him.
While everyone else is giving a totally correct answer of “do what you want and what seems fun”, for sake of completion I’ll give an alternative. If you’re looking for an optimal choice with respect to character power, there’s one specific point of the game where multiclassing is not recommended: exactly at level 5. At level 5, each class gets a substantial power boost. Martial classes get extra attack and casters get access to third level spells. Generally, these jumps in power are greater than whatever you’re getting from adding an additional class. Likewise, multiclassing at level 4 delays a feat/ability score increase, but this is a bit more manageable.
That said, this is pretty min-max-y. Yeah, being at Cleric 3 / Druid 2 would be weaker than level 5 in either class alone, it won’t be non-functional. You’ll still be able to play fine even if your build is slightly suboptimal. Even on tactician, as long as everyone in your party isn’t crazy multiclasses, you’ll be fine as the party can cover for any shortcomings on your behalf.
Lastly, you can always respect. At level 3 and want to dabble but still want to be built optimally at 5 or 4? Go for it, and then visit Withers when you level up for a quick respec. Bottom line, play how you want, experiment! You might temporarily miss out on a power jump, but it’s not crippling and you can always readjust if you feel underpowered