How large of a mash tun for 30 pounds grain? What size for 50 pounds ?
You also need to think in terms of the volume the star will take up. Data point…I have a 152 qt. cooler. I use for big beers. I can get 65 lb. of grain in it at 1.5 qt./lb. with room to spare.
Another data point. I have a 15.5 gallon keggle that I can fit about 33# of grain into. I did put 35# in it for an 11 gallon batch (1.3 quarts/lb.) of imperial stout but it was full to the brim and I won’t attempt that much again. When I make this the next time, I will double batch to be safe and avoid a royal mess in my brewery.