Ping worked (still connected via ethernet). I then set up relayd and luci-proto-relay and finished the configuration. I am now connected via wifi, but since it's the same SSID as my main router, how can I make sure it's working?
Got it all figured out; you need to manually download and install the relayd and luci-proto-relay packages, as the sysupgrade bin doesn't come with these by default. I set everything up via the command line, however after these two packages are installed, I'm pretty sure you can configure via the web interface easily as well.