by nvmbr
1) Yes, you don't need to play with a group, playing solo with 2/3 character can be challenging and fun as well. Play with more characters for added difficulty and more stress of keeping track of turns. As far as difficulty goes I would consider 2 player(easy),3 player (normal) and 4 player (hard).2) Avoid errors by rereading the rules thoroughly even if you are an experienced pandemic player.
3) Develop a way to keep track of turns as it can get difficult and confusing as time goes on. Place the character card upside down or facedown after you played its turn or make a "current player" token with unused chips.
4) Pace yourself when going through the campaign whether alone or with a group. Last thing you want is to be burnt out before even getting through half of the game. In my opinion, playing 3 games(3+ hrs) at a time can be more than exhausting for most players.
3) If possible, assign a player or two for upgrades after each session, this kills downtime where you guys are all arguing what upgrades should be made. Having only two players make the process easier/faster.
4) Assuming 4 players, each individual is responsible for disease cube closest to them. One person should not be doing all the accounting by himself. Also, having small trays can help organize little components and prevent them from being lost.
5) Enjoy the roller coaster ride.