As to M.2 NVME SSD you have 2 slots you can put any m.2 NVME SSD in there.
I only use Samsung SSD, others may or may not work I don't get involved with other brands
To replace keys Laptop Key Replacement | Keyboard Keys | Keypad Keys (replacementlaptopkeys.com)
Not sure if that does you any good In Germany or not its all I got.
1.Moving to M.2 from SATA Hard Drive its best if you can clone you HD to the new SSD.
2. Hopefully you have a full Image back up of your Hard drive is so you can just restore your image to you new hard drive.
3. Clean Install You'll have two options Set your BIOS SATA setting to AHCI and clean install normaly, they other option is to leave your BIOS Set RAID, in this case you will have to download The IRST driver from the Intel website Download Intel® Rapid Storage Technology (Intel® RST) User Interface and Driver
This is the driver that you need flpy-x64.zip
Start your Windows 10 install when you get to the part where it asks you to select your Volume to install too. there will be a link click that and browse to where you have that RST drive That should be in a folder that created on your Install USB just for this purpose so that you don't have to search very hard. Once you select it, it will install and your New SSD will be visible to select as a volume to install too.
Hopefully you have saved a copy of your eSupport folder as you can install all your Asus driver from that folder.
Thats all I got for you. Further reference Guide: How to install windows 8/8.1/10 The proper way (UEFI based installation) (asus.com)
one other very important thing Have Media Creation Tool creat your Install media, When you boot it up spam the Exc key, then select "UEFI USB" to boot from