Server setup for 1000 concurrent users

I'm building an online test/quiz website on Joomla! 3 which uses PHP + MySQLi on Apache (or nginx) at DigitalOcean. The quiz will run for 6 hours a day during working hours for a month catering to about 150,000 users in total.

My client says there will be 1000-1200 users at a given time taking the quiz. I'm wondering what kind of server setup would be necessary in terms of CPU and RAM or would there be other factors?

Currently there's a plan for $320 with 24GB Memory & 16 Dedicated vCPU at DigitalOcean. Will this server configuration do?