Dual channel or quad setup
Dual channel or quad setup
It's fine. Just like how no LGA1200 CPU is quad channel. You have 4 slots to add capacity. 2 DIMM's in a AM4 or LGA1200 board is fine. Filling to 4 DIMM's slightly increases performance, if (and only if) the DIMM's are single rank. (Memory speed has a bigger impact than this.) This means, don't worry about it. As long as you have 2 or 4 DIMM's, you'll see the expected performance from the CPU.
For 32GB of memory, choose 32GB regardless of the size unit. If you're not requiring that amount, opt for two 8GB modules.