It all depends on the size of the tank and the temp outside. As the temp gets lower the total BTU a tank can supply gets lower. You need to total the BTU you want to be able to use at one time (regardless of the number of burners that covers) and base the design off of that.
You can use multiple tanks connected to a single manifold. Nothing fancy required. Just add a T and connect another tank. You can connect ahead of or after the regulator, either way will work. If you connect after the regulator, you can't guarantee that they will both supply equal amounts of gas, but of one can't give all the system needs, the other will help make up the shortage.
You can get a big tank (likely a 120 gallon, or a 420 pound cylinder) and run the burners off of it. You would have to talk to the propane company and tell them what you are trying to do. They can put the correct regulator on the tank for you.