As you can see here, the forums module is capable of hosting over 100 forums and loading them with little issue. It seems you understand that initial startup will take longer then new visits. I am not sure which version you are using, assuming the latest, but the expand/collapse per group has not been part of it for some time. Even if it were still there, it would still be sent to the client browser as it used javascript so this would not reduce code. As for usage of v13wstat3, the module is using v13wstat3 in as few places as possible.