I use a handful per 20gal. Never have had any issues.
As for pumps, I'm using a Rule360 which is a tad too much for my 25gal set up but is working out. It is generally the goto pump for most applications. You want good flow that your bait can swim in and not be blown around too hard. Venturi is key for air and a must have.
One note, I wouldn't use a defoaming agent. Some guys swear by it, but it hides an issue that can kill your bait. If you're getting foam your bait is stressed and you need to fix it. Either more air, or cooler water, less current. Foam will keep the water from exchanging air waste products with the atmosphere, in addition to indicating stress.
Keep 'em cool, keep 'em oxygenated, and keep 'em moving at the right speed and you shouldn't have any issues.
A potato chip or cheeto will get rid of bubbles cheaper than foam off.