Could you pl. elaborate on what "more enterprise ready" means. I understand that the single VPS server you have is already enterprise ready but you want to be more enterprise ready by separating it in two: "One for moodle and another for our MySQL enterprise version". Where does "HA in future" come to the picture? Is each of them is in turn a server cluster?
You ask for the size of RAM - no mention of the load(?) Did you read the documentation to this forum?
I went through your previous discussions https://moodle.org/mod/forum/user.php?id=1324621&mode=discussions&course=5 and must say they cover a vast set of software and architecture, anything from MS SQL-Server to Oracle, from Moodle to Canvas, from load balancing to fail-over,... That's a handfull!