» Question » Are all flashpoints designed for 4 people?

For the most part, yes. They are all balanced for 4 players.

The only exceptions are The Black Talon and The Esseles, the first flashpoints for Empire and Republic, respectively. Those two are designed for 2 players and their companions, so their difficulty is lower. In fact, they are soloable by most classes+a companion by around level 16 or 17.

If you're wondering about operations, which have various modes ranging from 8-man to 16-man, then those are all at level 50.

The higher level flashpoints are never for any more than 4 people. However, there are operations for max level characters. These are TOR's version of raids. They are for either 8 or 16 players and have multiple difficulty settings.

As of right now, as far as I know, the level 50 "large flashpoint" is called an Operation. The only one I know about is called Directive 7 and it allows sixteen players. Both factions have access to the same Operation.