Small containers are good for a variety of reasons, the main one being that over-potting is the source of many issues for people just starting out. I had the pleasure of finding that one out the hard way. Since I don't veg for very long, 2-3g pots work wonders for me because they get rootbound fairly quick and are ready to rock and roll much faster than 5-7g pots.
I do the same as you when I do this. While I have plants in the pots, monthly top dresses of compost and amendments until I harvest. Then dump the pots, re-amend, and mix a bit of extra compost and perlite and you're ready to go again. I love how cheap things are this way, only need to pay maintenance costs to keep your soil going forever. I've been using the same soil for the last 3 years now in fact.
The main thing that screws most of us is the plant counts in our respective states. I was only able to have 12 until becoming a caregiver, now I can have 24. As you said, variety is the name of the game and it's tough maintaining variety with low plant numbers. Especially when each mother and clone counts toward your plant count and reduces the amount you can have in flower.