Yeah I don't think having Masters and GM players in Tier 3 will work.. you might want to split and try and get a third M/Gm team or move your Plat/Dai/M/Gm players into Tier 2 and some of the plats can probably play in Tier 4...
The only possible issue that I can see with the M/GM team is that some players may show up, but if you can clear up that issue then the M/GM team should be fine. Either of chad's suggestions should work.
Another option would be that you can take some of the golds and have a T3 team of plats/golds, while moving the rest to T2
Even the smallest donations help keep sc2sea running! All donations go towards helping our site run including our monthly server hosting fees and sc2sea sponsored community tournaments we host. Find out more here.