OK, first the flaps -- and HRV is usually installed with 2 flappers to "balance" the air pressure with the outside air. Due to imbalanced duct lengths and other pressure issues, the flaps get partially closed to get the right air pressure.
By all means none of the flaps should be EVERY fully closed, and having one closed would acutally cut the flow down much, much more than half.
IE: if the exhaust air was closed -- the air pressure inside the house would be higher that outside and the incoming air fan would be "working uphill" and not move much air. If you thing of your house as a big long pipe with a fan at both ends and a flap, if you close a flap the air flow drops A LOT.
Next, the condensate -- this depends a whole lot of the humidity of the house air, the outside air and the air temperature outside. I don't get much of ANY other than a few drops a day unless the outside air temperature outside is colder than -10C. Once it hits about -20 outside I start getting around 1 cup a day.
Most of the humidity goes out with the slightly cooled air. Colder air holds less water, but if the inside humidity is 40-50% and then you drop the temp to 0, you will get a bit as the condensate only really happens after the humidity hits 100%.
IE 40% at 22C, dropped to 0C will hit about 90%, if it hits -10C then it goes above 100% and everything over falls out. On my HRV it has a "high" setting and a adjustable "low" setting, which can be hooked up to a humidistat to kick into high if it gets to high.
In the end -- most of the water vapor goes out the vent, not out the drip tray.
As for capacity, I used to have to use a towel to clean out each of my window tracks every 2 days or the water would start running down the wall and soaking the carpet with my 200 gal tank. With the HRV on, If I get fog in my 35 year old metal frame windows -- it means it is colder than -25 outside. You should be able to keep the moisture level down in a house with 3000 gal to a reasonable level --- but you might see a small could form around the outside vent
