Gegenpressing means that front 4 have to do a lot of work - obviously pressing high up the pitch but also tracking back if the press is broken and then countering quickly back up the pitch if the ball is won back. I'd say Klopp has been very smart getting depth in those areas. He's probably intending to rotate those players to keep their legs fresh so Liverpool can play the way he wants. The answer to the question of how they all fit on the pitch at once is that they don't - combinations of them do.
Gegenpressing is the one reason to keep Lallana - he seems to have adapted to it faster than others.