My two Calamondin trees are putting up blooms plus new leaves. But there are very little new leaves, maybe 3-4 on a new branch. I thought that the spring flush should be the most efficient, I've seen pictures that show 10+ leaves growing on one branch... Is this normal? Is it going to be followed (when the blooming ends) by a major vegetative growth flush?

Yes its normal...growth can come in prolific flowering or leafs...Can also be bienial(spelt wrong)....i find if you let a lot of fruit form one year it can hinder flower production the following year...you might find your next growth phase will be more leaf growth.Just make sure you thin some of the flowers out as citrus can be greedy in that area.
Make sure they are getting nitrogen....very important for spring growth.
A fert with 5:1:3 NPK is ideal....some fast acting N and some slow release N pk plus trace elements.