Yes, you don't want 4 x8GB. 2 x16GB is much better, giving you the same memory capacity while reducing the stress on the internal memory controller that comes from having four DIMMs installed. You also still get dual channel operation. Four DIMMs tends to be harder to achieve XMP profile speeds with, increases CPU temperatures and in some cases creates stability issues with the memory configuration that require a bump in DRAM voltage, further increasing IMC stress and CPU temperatures.
Always use two DIMMs when possible. Four DIMMs should always be a last resort when the desired capacity cannot be obtained using only two.
I'd also shoot for 3200mhz sticks, preferably with a CL14 latency.
I like the G.Skill Trident Z sticks, or even the Ripjaws if you get them in CL14 or 15 models. The Corsair Dominator sticks are good too.
Also, personally I'd recommend looking at a higher end motherboard. That Z390-A Pro is a budget board, intended more for lower tiered 9th gen CPUs, so even though it technically supports it you could definitely run into issues if you you plan to overclock or run long duration sustained boost loads with that 9900k, especially if your cooling isn't up to snuff and while on that subject it would be helpful to know what cooler you have because coolers that might have been deemed "good" for older CPU generations tend to fall to the ground and curl up crying when used with the 9900k.