Manually defragging an SSD (which is not generally necessary provided your disk controller is set to AHCI mode and not Native / IDE) should take all of a heartbeat or two as it just basically runs the TRIM function manually and should not do any irreparable harm to your drive.
As far as keeping files / data (music, pictures, vids / movies, etc.,) on a separate drive? I would strongly endorse it, where ever possible.
Personally I have three physical drives in my computer. An SSD and two Spinners virtually everything is on one of the two spinners.
That accomplishes three things (in my opinion)....
It simplifies my backup strategy.
It leaves me more room on my SSD.
It protects me, to some extent, against some catastrophic failure of the Operating System, should a reinstall become necessary.
AND that concludes what is very subjectively my own personal opinion.