You need to prepare for the high load on US election night 2018.
You should do load testing and other best practices (like renting additional servers, or using more caching). I would assume that load will be equal or greater to that on election night 2016 during which time the website was barely responsive. I recall trades taking 30 minutes or longer to execute.
I've also seen the website become unresponsive at other times - notably the AZ Senate special election (2017).