In case you have chosen WordPress for MVP it’s better to go with existing solution for community, like BuddyPress. While it’s ok for MVP except issues as the userbase grows. At some point you will need to migrate data to some other platform and it might not be the easiest task.

As to what could be used for the tech stack - I would recommend to go with technology your developers are familiar with. Please note, it will be easier and less expensive to find developers familiar with php/mysql than, for example, JS stack. So keep that as a consideration.

There are few scripts/platforms for communities already available. But the quality of code/architecture differs.