I already played in 6 at the same time. I won one in 2 place and another in 5 place the others I lost. but I think it's worth it if it's freeroll tournaments or small-value tournaments.
I try to play no more than 2 tournaments at a time. But earlier I played in 4 tournaments, it does not allow you to concentrate, and does not bring satisfaction. The first rule of game - Have Fun.