I'm no expert on the technicalities of this, but I have a 22 gallons Rubbermaid tub. I fill it within 5" of the top, don't know exactly how many gallons of water is in it, but I've never kept over 6 or 7 dozen at a time in there.
If you give the fish some cover, such as broken clay pots and rocks to hide under, they will live much longer. I noticed without cover, I'd get at least one or two dead minnows a day. Now I only get one dead minnow every 4-5 days. I bought an old cheap aereator at Walmart, I know there's a better setup than this, but after the weather gets into the mid to upper 80's I'm gonna move these to the basement. It's difficult to find minnows in my neck of the woods without driving 20 miles, so I try to keep a few in stock. On hot days I'll throw in a gallon milk jug full of ice in there, jug and all, let it melt completely then put it back into the freezer, if I feel it needs cooled again, I'll throw anyother one in there.
I run the aereator about 1/3 of the time and feed them oatmeal. I keep another tub next to the full one, and when it comes time for a water change, I'll take out the rocks, siphon or slowly pour the stale water out, and transfer (dip net) them into the other tub. Make sure you transfer the rocks and clay pots to the new water first so the minnows will adapt to their new home first. I don't use a filter, and this takes a lot of work, but saves me driving 20-30 miles out of the way.