The party size never bothered me. Probably a combination of (a) that's the game setting so I assume it's balanced around that, (b) I've played a ton of 4-man co-op games so it's a natural group size for me, and (c) in my experience, four is the sweet spot for a 5e game where each person brings important and non-redundant skills and less assertive characters aren't getting pushed into the background (and before combat turns into an hour-long slog). Obviously individual preference and experiences may vary. While some of this isn't a problem when you're in control of all the characters, a four player group sits right with me.

The BG3 creative lead recommends a custom character for your first play through, an Origin as a second choice (but thinks they're better suited for subsequent plays) and doesn't recommend Dark Urge for your initial play at all. I can see that; I think that if I started Dark Urge I would have bounced off pretty quick. Not because I'm terribly squeamish about pixel murder but, without context, the bloodbloodblood aspect would have felt entirely nonsensical and tryhard.

On the other hand, the dev said that playing a resisting Dark Urge could be the "most heroic" play through. I'd have to see that in action all the way through since deciding NOT to set orphans on fire feels more like normal non-psychopath behavior than 'heroic' but maybe it shows more depth later in the story than I am.
Spoiler: Dark Urge Stuff
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I cheesed the Alfira murder by throwing a Sleep on her in the Grove and bonking her unconscious and getting the silver Dragonborn rando bard instead. Mainly because I want Alfira's robe later and since every online mention of the poor girl gets people saying "She joined MY party as a Dark Urge, EH? WINK? WINK?" there wasn't exactly any mystery there. I'll politely ignore the "This person was stabbed a million times and placed in an elaborately drawn blood circle... pretty sure a wild pig did it" part.

I did think that getting a magic item as my reward was interesting and the incentive to murder people for more magical items. But then the game throws so much gear at you that it's no struggle to turn your back on it anyway. Astarion got the cloak anyway to assist in his stabbin'. Maybe my weird Bhaal butler guy should go talk to Astarion instead.