It depends on how the pace you want the game to go especially with a 50 person tournament. Alot of those large types of tournaments we usually had around 1,000-1,500 in chips and the blinds would increment from 20-30 minutes. In terms of your blind structure 20-40,30-60,50-100 and so on but basically the higher you raise your blinds per interval will make the tournament go faster. Normally a final table will consist between 8 and 10 players. I hope that helps