This official community was running on a 1 vcpu 1 GB memory droplet on digital ocean for years until it got ddossed. It is very unlikely that flarum caused 100% usage, but it also depends a lot on the resources the VPS has and the attention your community gets.
One more thing I would like to point out is that you need run Flarum with debug off (check the documentation), otherwise assets (javascript and Stylesheets) are recompiled on every visit.
