I can always export additional assets at 16x16, 20x20, 24x24 in one simple click.
Well, yes and no.
Going from 32 to 16 will usually go well (especially if you use a 16x16 grid overlay to check how it turns out at 16), but going from 32 to 20 may cause some unintended blurriness.
A little trick I taught myself, is that if I e.g. aim to create icon sizes 16, 20 and 24, I start with a 240x240 canvas.
That can be divided by all three icon sizes. (just use appropriate guide layouts in PS to check how things will turn out for each icon size)
But considering the amount of icons you are preparing, that would be a ridiculous amount of extra work and tweaking.
B.t.w., looking at the quality of your work, I am not assuming I can teach you anything, I just thought to share my thoughts.