QNAP - SSD buying/configuring device.?

[nojunk]

I recently purchased a QNAP 453D for a great price. I have installer 4x4TB. I also bought a QM2-2S-220A to hold a pair of M.2 SATA SSD Expansion Cards. I have a series of questions ... thanks in advance for your responses.

NAS Purpose:
-File server for home businesses - nothing special.
-Plex for watching a various movies on home tv ( 1 4K TV) most movies are 1080P
-Photo organization (likely QuMagie App - but I have not played with it yet ) (200 K photos)
-Backup for various devices.
-VMs but not for the foreseeable future.
-Surveillance down the road.

How to configure SSD
Should I run them the 2 SSDs as 2 RAID 0?
In using Cache why would I ever configure RAID 1?
How much cache? How much for storage/Apps?
What Apps should I install on the Application Volume if any? for QuMagie? Plex?
I plan on buying 2 x 500GB. Should I consider going to 1 TB? what questions should I be asking myself?

Thanks for your help, I look forward to adding value to site.