Are the holes in this colander small enough to strain cooked rice without losing the individual grains?

I don't know. Let's find out!First I'll Measure the holes using a Drill Bit - 5/32 of an inch. About the size of a fat toothpick. The holes are round at the bottom of the colander but stretch a little to an oblong shape as they go up the sides.Next I'll pour in some dry uncooked rice. I have Minute Instant Whole Grain Brown Rice (Cooks in 10 Minutes) in the pantry. That'll have to do. I pour 1/4 cup of dry uncooked rice into the colander. I stir it and shake it around a bit. About 15 - 20% of it falls through.Now for the cooked rice. I follow the instructions on the side of the box.1 Cup Rice1 Cup WaterBoil for 5 minutes - Simmer for 5 minutesAt the end of the cooking time, I pour the rice into the colander and repeat the stirring and the shaking - no rice falls through. Not a single grain.So the answer to your question is YES - the holes in this colander are small enough to strain cooked rice without losing the individual grains.(That was fun - thanks for asking!)

ATK recommends this colander, but I don't know which size. Is the 3 qt. big enough for most needs?

This is the medium size. Big enough for most needs, but not all. If you're cooking pasta for 2 or even 4, you're probably fine. If you're cooking pasta for 8, get the big one. I have all three sizes and use this one 95 percent of the time.

Does the base, where the stand covers, also have holes?

Yes. The stainless ring is a thin ring holding the colander and it is solid so there wont be any leaking on the side of the bottom through the ring, but the base or inside between the ring, which is the bottom of the actual colander, has holes to drain through the bottom, between the solid ring that actually touches the surface that the colander sits on.