QNAP - SSD buying/configuring device.?

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.

First you need to decide between the following options:a. Cache acceleration (some variants exists here: read-only | read-write, small blocks only | small & large blocks)from my experience, Cache acceleration will do something, but depending on the settings can also cache a movie file that you don't want to watch too soon again, so caching it was useless. Cache acceleration don't have the granularity setting to specify for which particular folders you want to have it activated (QTier have this)b. QTier - somehow good for making parts of the storage fast, is not on the fly and does not predict what will be the next file/block you'd like to have it served fast (from the SSD instead of the cold storage - HDD). I'm not sure that the Cache acceleartion has a predictibility feature (e.g. if you start to read/play a big file from the NAS, the first part is served directly from HDD, but while you're watching a movie, the SSD is copying the rest of the file into the cache so the rest of the file will be served from cache).c. Create a storage pool (RAID 1) only with the 2 SSD disks, make this step first (before creating the DataVolume on the HDDs), and create the first Volume on the SSD Storage Pool, so this will become the System volume (where the applications will stay). If the first volume created on the NAS is on the HDD Storage Pool, that will become the System volume, and it will take other steps to try to move the apps to the desired volume (on SSD).After using the first 2 variants for some time, now I'm trying to work with the last variant, using a pair of Nvme Samsung 970 PRO 512GB. I will use this volume to host all the APPs, the VMs' virtual disks, and everything that I would like to have it as fast as possible.Fast I mean not only from the NAS to my network clients (although, I'm using a 10Gbps link for the NAS), but fast in terms of CPU <-> internal storage. You can find a summary and differences between QTier and SSD Cache here: https://www.qnap.com/en/how-to/knowledge...comparison although one major difference is missing: the option to select for which folders you want to have activated SSD Cache (That QTier has).Coming back to your questions:RAID 0 for SSD Cache read-only is not a problemRAID 1 is a must for SSD Cache read-write, or for QTier (that has write cache feature by default)My experience with QTier (RAID 1) was finished not nice: I've removed one of the SSDs from the storage (having it off for some months) to use it temporary in a notebook, when I've finished using it I've erased all the partitions and put it back in the NAS as a blank SSD. Well, the "unhealthy" RAID 1 in SSD was not recognized correctly as unhealthy by the storage and it damaged the data from the System and DataVol1, so I had to erase everything and restore from backup. Not nice, taking in consideration the amount of data and all the custom software I had installed and configured.From the recommendation of QNAP article, you can't go wrong if you will use the option SSD Cache acceleration for "Home usage, where the NAS will be used for a large range of different applications". depending on what kind of files you want to have it cached you should choose the option Cache Mode (only small blocks or any).If you want to use the SSD for write cache also, use a RAID 1 setup for your SSDs, so you will not have corrupted data when one of the SSDs will fail.