yeah, i've found quite a bit of conflicing info online..
tilapia can start breeding in 3 months..

at some point i am going to get some, but right now i'm getting my feet wet using bluegill and yellow perch

if you can't do a sump, maybe you could adapt a "barrelponics" type flush tank above your growbeds,
my outdoor system is 2 barrels (4 half barrels) gb's, and a 110 gallon rubbermaid stock tank for the ft, my water levels only fluctuated a few inches. another plus with this type system is that my pump is the power of running a small 40 watt pump always on..
i don't think you can really oversize the pump, you could divert part of the output back into the fishtank to add aeration, and flow. if using a "large" pump you could put it on a timer and pump, say for 15 minutes every hour-as long as the volume is about equal to your ft

the large stock tank in your basement sounds like the best bet for wintering your fish, but that much water will be harder to heat, so invest in some insulation for around your tanks, whichever way you go