Win 10 Home Vs Pro Features
Main Pro features are Remote Desktop, Domain Join, Bitlocker and Hyper-V support (install an optional feature to be able to create and run VMs on your desktop).
I use Pro at home for the ability to RDP between my different computers and Hyper-V to run some Linux VMs on my desktop. If you need/want any of these features, Pro is great. If not, Home will be just fine.
Enterprise Mode Internet Explorer (EMIE) could also be of interest on a poker only PC (super locked down, secure version of IE) but I'm not sure if it works with current sites. It would probably be painful as a primary browser on a general purpose desktop due to all the disabled features and restrictions for security purposes.
RE #2: The main point of an SSD is to access data more quickly, especially random access usage. A secondary SSD would be faster than an HDD but you'd have to pinch your budget somewhere else. A fast boot drive plus a secondary spinner is a perfectly reasonable config here.
Backup is a separate concern you should address. It is preferable to write your backups to an external or network drive that is not connected when not being actively used for backups. Quick version would be get a 2TB USB 3.0 drive and back up to it once a week. Keep it in a drawer in between backups. Better version is to get 2x 2TB USB 3.0 2TB drives and alternate which one you back up to each week. if you can keep one of the backups offsite, so much the better. I like to add a cloud layer for my pictures and docs. Office 365 annual subscription comes with 1TB of OneDrive storage, you can also consider Google or DropBox.
RE QVL: Part of the issue is that JEDEC specs have not kept up with the RAM speeds that are commonly in use. The rated speed of most RAM these days is based on its XMP profile and is technically overclocked. RAM on the QVL means that the motherboard manufacturer has tested that kit with the board and confirmed the speed it will work at. Other RAM may work just fine and will almost always work at the fallback JEDEC speed (probably DDR4 2666).