I used a HDD for storage, SSD too expensive and suffers from being written too, not worth the downsides to store photos/music imo - not like you notice the difference
250 ssd for os and main programs is a minimum for me I had a 120 and filled up Quick. But an ssd is one of the best upgrades you can do huge improvement in Windows and even more in Linux
It's 2017, you can't really a well performing PC unless you have SSD to at least put your OS and applications in. Using HDD for OS is just way too slow nowadays.