Ok, got up early so will get started on this set. At this point I would not send out any stacks to attack cities that does not have at least 2 top defenders (4) and 1 or 2 second tier
defenders (3).
Three top defenders is better, as you saw they hit the stack and now you have no defenders. With strong defenders the stack has a chance to move into position and not be attacked on the way to its target.
If the stack was mostly knights and a single arq, that would not be too bad as they are not weak, but char/enslavers/monks/ac and maybe even WE are weak defenders at this stage and weak attackers (maybe not the WE) against most units in a city.
I am a fan of elite units, but I am not fanatical about them. IOW a 5/5 char has limited value right now to me. It can cherry pick weak or damged units from towns that it can get back and recover or no other units are there to counter them.
They are not much in the open field in hostile lands. It figures to take damage and not be able to fight for several turns, IF it wins. That is fine in Venice, not so fine on the road to Rostov or other towns in hostile territory.
A knight is more likely to win and less likey to take a lot of damage. It will soon be elite, to me I would not take chars on the road. Leave them where they have better odds.
Later knights will fall into this category as we face stronger units with defense 5 or 6.