Does the game use different cards for the 2 sides or are some cards able to be used by either side? Trying to decide if the core game could be used for 2 players or if we'd both need a copy.

For example, L5R uses personality cards for the factions, but shares the rest of the card pool for playing...

The core set (on its own) is perfectly viable for two players, providing they don't want to use the same factions.

There are 20 card sets for each of the seven factions and two 10 card sets of the neutral factions. For two players you would pick two factions each and a set of neutral cards to play. There are plenty of options for two players there, just not a lot of serious deck building.

My group (7 players) plans to buy 3 Core Sets.