Make Magento store hosted at DO visitor peak proof

I don’t know if this is the right place to ask this question, but I currently run a Magento store on a DigitalOcean droplet. We are seasonal business and we expect a huge visitor load the next 1 - 2 months (christmas season).

Last year we had a hard time staying up, everything went slow on some days. A single page load would take like 50 seconds one we got like 40 concurrent visitors.

I now upgraded to the DO plan with 8GB memory and 4 core CPU. I then did a stresstest but still the shop has troubles with large amount of visitors.

On the Magento side I already:

• Installed FPC
• Optimized (disabled) modules that we don’t use
• Setup REDIS caching

We use a seperate database server, it is a 1GB memory droplet and multiple stores are associated with this database server.

I am hoping on a couple of simple tips & tricks. Where should I look or what can I do to optimize performance on times with large amount of concurent visitors.

PS: we are expecting around 200 concurrent visitors on our peak.

EDIT: the webserver uses Apache, database server uses MySQL

Thanks in advance!