Jitsi-Torture - Server requirements

Hi
I am looking to setup Jitsi-Torture to stress test Jitsi we have setup across multiple Video Bridges
We will be looking at setting stress testing 40 users per room but 10 rooms in total, so around 400 concurrent users.
From reading on the forum, the most cost effective way to do this would be to use AWS Autoscaling, and only have the servers up for when we are running the tests.
My question is, for the above setup what server requirements would I need for the Selenium Grid and for each node?

Thanks
JLU