As far as I remember, your companions will only attack if the npcs are hostile with the exception of boon. Boon will always shoot legion on sight. You can have some decision over their actions though by talking to them.
As for the armor it does matter when and where you have it on. Again my memory may be foggy but factions can be peaceful or aggro depending on what you are wearing. You can even go into a camp with hostiles if you have their faction armor on.
Take all of this with a grain of salt though, it’s been a long time and I did play with and without mods.
No, they aren’t. DLC is an expansion upon the content. The best case scenario for mtx that do not affect gameplay are cosmetic only.
If a game in any way has anything else than cosmetic mtx, the game is worse.
“But you don’t have to buy it!” Is how I often see them defended, the subtext being that, if I don’t buy them it doesn’t affect my experience.
Here is the secret, games with mtx are designed to have problems and they sell you the solution. They are designed WORSE intentionally, so you will spend money to bypass the inconveniences. Often your time.
A perfect example is something like long standing games selling boosts to max level. They’re aware the old content is dead, and they’re aware the only people playing it are the people who don’t want to spend money. Why don’t they fix that?
The answer is they did, they decided that inconvenience was acceptable in their game in order to convince the player to spend money.
MTX is not content, often it’s used to bypass content or save time. DLC is content. DLC often expands upon the experience of the game. MTX worsens the experience of the game just buy existing. Dlc doesn’t change your experience if you don’t purchase or use it. MTX changes the game at a base level no matter if you spend money or not.
Larian (baldurs gate 3) is massive for being indie. I think where your misconception comes from is the term indie. The term comes with a lot of predetermined expectations and definitions, but in spite of this fact very large studios can be indie.
Of course it feels weird to label a studio as large as larian indie when compared to the likes of supergiant(hades) or two brothers of bay 12 who created dwarf fortress. None of the three are technically any less indie, but one certainly feels more indie, doesn’t it?