No experience but jellyfish are supposed to be extremely hard to keep - or at least take a lot of research and provisions. I believe some can still get stuck to the sponge filters and die, yet they need good flow. They also can't be in tanks with sharp corners and are particular to lighting. I also believe keeping multiple can end with them getting tangled together or something - at least I remember hearing that at least some have to be alone, or at least when in medium to small tanks.
Jellyfish are also expensive and have short natural lives anyways, I think. Not trying to discourage, but they are hard to jump into. :fun5: Good luck if you decide to go through with the tank.