Ultimately you won't know until you fly it, but there are a few things you can do to estimate performance. You can measure the power use with a watt meter, but that only tells you how much it could use at various throttle settings, not how much you'll actually be using.
A useful rule of thumb is you need about 50W per pound to fly simple circuits with gentle climbs, or 100W per pound for aerobatics. So a 1600W motor can do aerobatics for a 16 pound plane and your maximum weight will be 32 pounds. If the plane is lighter than that, your power draw should be lower, unless you're blasting around at full throttle all the time.
Those are large models. A typical club model is more like 5 lb. Generally people don't build much bigger models until they've got a lot of experience, because (as you've noticed) they get pretty expensive.
80amps for an hour would require an 80Ah battery, so for a third of an hour (20 minutes) you'd only need 27Ah. You should probably add an a safety margin, as discharging below 15% reduces battery life, but even a 30% margin only brings you to 35Ah.
BTW, a 4s battery is only 14-16v. Multiply that by the maximum your ESC can handle (80A) is only 1280W. To get 1600W you'll need a 6s battery.