You should know how many SSDs, Ram and HDDs you want to put in. On the list there is only 1 of each

In principle, your list already fits together...

The Samsung 990 Pro is a bit too mutch in terms of performance for a DS923+ for what it can do.
I would rather go for a WD Red SN700. WD Red SN700 (1000 GB, M.2 2280)

With non-original Synology RAM, you may get a warning with a DS923+ because it is 3rd party RAM. However, according to the current status, there should be no restrictions. see e.g. https://nascompares.com/guide...