Hi lodl, nice site!
One tool that I have started using recently to help determine if there are additional optimizations a customer might make to their site is a chrome plug-in called “Is it cached?”. Once installed it becomes an additional tab in the “Developer Tools” dropdown and it can tell you if there is content that you think should be cached and isn’t (and perhaps help you figure out why). For example on your site I see that there are some assets which have a query string associated with them that aren’t cached (which matches your settings). That may be intentional; I don’t have enough experience with your forum platform to tell you what the impact of ignoring query string might be… but for some sites ignoring query strings doesn’t cause an issue and so that might be a few additional objects which could be cached.
Obviously if those query strings give unique per user customization then it’s not really an option to ignore them.
The site seemed to load pretty quickly for me when I visited, how do you feel about it’s performance overall?