Bluegill spawn several times yearly, as many as four or five times, depending on geography. Farther south? More spawns. Bluegill can mature as small as 2.5 inches in length, six months old. But, those young spawners only occur when there are few larger fish. Bigger males keep younger ones off the nests, by competing for that nesting space. Rates? Depends on fish size. Bluegill can lay as many as 2-3,000 eggs per spawn.
Catfish spawning in a one acre pond? Sure, they can. Don't encourage it. If catfish spawns are successful, you wind up with too many. And, catfish will quickly outgrow their environment. I get calls every August from people who have had catfish die offs, due to overcrowding. That's the bad news...here's the good. When you have bluegill, catfish spawns are less likely to survive. You see, catfish spawn last each year, and their little babies are mere morsels for an aggressive bluegill.
So, look at catfish as a "put and take" fishery. Stock some, grow them, plan to stock more. Bass and bluegill will reproduce, survive, create a food chain. Catfish are quite as successful at it.

Teach a man to grow fish...
He can teach to catch fish...