The party of 2 is a good question. Community Update #6 revealed that there a Lone Wolf mode is planned but will Not be available at the beginning of EA. So you'll be playing with 2 characters where everything is balanced for a party of 4. Thus, your ability to play (on the single difficulty level offered during EA) will heavily depend on whether BG3 uses a party or individual experience point system. Does everyone who participated in a fight get the full experience points? Or does everyone get a fraction of the total exp (total divided by # of participants)? The latter will mean your party of two will level up faster than a party of 4, which might compensate for the lower amount of actions your party of 2 will have.
https://youtu.be/1zO9K6bWu3c?t=54 (from May, so very out of date) implies the former, which means that a party of 2 will be fighting at half strength the entire game.
That said, buying the EA game gives you access to the full game when released, so you might as well buy it now if you're not strapped for cash. Lone Wolf will eventually be added according to Larian. Plus, playing as a party of 2 will give Larian (probably-useful) data on the ability of players to play with <4 party members.
