For the size batches you are talking about, you'll want 5500W elements, which draw 23A. So, to run one element, you will need to have a 30A GFCI protected feed circuit. Two run two elements simultaneously, you will need a 50A or 60A GFCI circuit, or two 30A circuits. Probably cheaper to put in one 50/60A circuit than two 30A circuits. If you plan to add heat during the mash, you should recirculate, which will require the addition of a pump. You could build one 30A panel now and another later, or you could start with a 50/60A panel design, and only put in enough of the components to run one element to start.
Lotta possibilities, but it's up to you to choose how you want to proceed, and then go with an appropriate control panel design.