Suggested internals for a new laptop?

Hey r/buildapc!

I just got a new Gigabyte AERO 15 and it came with a pre-installed 256GB SSD with some mediocre r/w speeds, and a single 16GB RAM blade. The specs say that it has two slots available for physical memory:

2 x M.2 SSD slots (Type 2280, supports NVMe PCIe X4 & SATA)

And two slots available for RAM:

16GB DDR4 2400 2 slots (Max 32GB)

I was wondering, what are my best options for filling these available slots? Here's some extra information, to (hopefully) help narrow down the search:

• I would prefer two SSDs, as I want to dual boot Arch/Windows like I do on my PC (and I play games on Windows, so it's going to eat up a lot of memory).
• I don't really need to fill the RAM slot immediately, but I'd like to eventually since I have the space and I could use the extra ram for video games or work.

P.S. an unrelated question: which is better for gaming, Windows 7 or Windows 10? The laptop came with 10 pre-installed, but I've also got a bootstick for 7. I'm not that into 10 from a privacy/security perspective, but I'm also not doing anything except gaming/using Microsoft-specific software on that partition.