You just want an SSD right? Were you telling me you can recycle your old SATA hard drives? I think it has been almost a year since I first recommended that system, so I forget. How do you want to do Windows?
(1) Retail copy -- You get phone support... which is probably useless
(2) OEM copy -- No phone support, often $20-$40 cheaper than retail but it's tied to your motherboard forever (eg, you buy a new motherboard, you buy a new Windows... retail I think you can use on another board if you replace it)
(3) Pirate -- Free and Microsoft publicly publishes the SHA-1 hashes for their iso files, so you can know whether a Windows ISO you download has been injected with malware or not
Whichever of the 3 methods you choose, it should be Windows 10 64-bit. There is a fourth grey market option I don't recommend
(4) Reddit software swap -- Get a Windows 10 key for $25 or so
Because if you're not going to buy a legit copy you might as well just pirate for free instead of paying some asshole $25 for a key.