Update:
Got the Rpi 8gb version and kit from pibox.com
Came with noobs already installed in the microSD. But later found that omv needs a non-desktop version of raspbian OS. So formatted the microSD and installed lite version.
Purchased a powered USB hub and 1 sata-USB3.0 connector. Installing Plex - tried initially using docker, but don't know why that didn't work at all. So installed plexmediaserver directly without docker. Copied few 4k HEVC True HD movies and disabled transcoding on Plex. So far, all looks good.
Want to give spl thanks for the guidance guys. Now, will put the old laptop for sale (to tally the RPi purchase amount
)
Now, planning to purchase a bigger capacity drive. Should I get a normal 2TB drive? Or should I get a specific NAS drive? Usage: Mostly Plex, other times - file storage. Just saying, I won't be reading/writing on the drive 24x7. Any suggestions?