In terms of carrying barrels - its fun to do it if you want and nobody is forcing you to carry them around - as far as I can tell the encounters are beatable without stacking barrels.
Can you stack them if you want - sure, why limit something that is optional.
The amount of surfaces is ok for me, albeit on the larger side.
Because even if you choose not to use them, there are so many that they inevitably go off from aoes, or enemies.
There are a few locations with barrels as far as I am aware - the goblin camp, the Zhentarim hideout, and the underdark if you count the mushrooms as barrels? Maybe I am missing others, but those are the ones that stood out in terms of exploding barrels.
But there are plenty of encounters with no barrels, and numerically there are more of them I feel than ones with barrels.
As per the combat log Fire bolt is strictly better. Does 1d6 damage. Another 1d4 for the burning. Then on the enemies turn they take an additional 1d4 for burning and if the enemy then chooses to move through the fire, which they often do, then they take another d4.
I mentioned it in other threads Firebolt is strong for now. But the 1d4 is the Burning status, which is not tied to FireBolt directly. The burning damage does not stack and I suspect that FireBolt will increase to 2d6 at level 5 as opposed to 2d10, making BG3 firebolt slightly weaker than the 5e one. Granted, they could remove the burning area from FireBolt and put it onto Create Bonfire, which would make more sense to me, but that would mean you would be stretched on cantrip choices.
