SSD for the OS. It does have to be that big either. I ran W10 on 128GB I bought two years ago before they got cheaper. The rest of the machine was about 10 years old at the time.
My Current PC has a Kingston 120GB SSD for the boot Drive
I still have an old Netbook, that came with win 7 Home Prem. installed, and I was able to upgrade it to 10, it only has a 32GB SSD. and it runs..painfully slowly, but it runs. it actually runs 10 a little better than it did 7.
(I actually bought the Kingston to upgrade the netbook, but upon disasembly, I found out it takes an M2 SSD, not a SATA, like i had bought. this PC needed one anyway..)
also, if you like Seagate and have had luck with their products in the past..more power to ya. Me personally, I've never had a Seagate that didn't fail within a year, and twice, right out of the box...
on the other hand, Western Digital has NEVER let me down. (but I know people with the exact opposite experience...so...YMMV...