Uff!
You can add mods as you wish, those that you consider necessary for your forum, for the type of end users you plan to host...
First of all relax and enjoy the ride, with the time you will learn and decide in your own what is best for your venture...
There's not 'must have' hacks, although you may focused on security first... from 3.6.4 most of the hacks work with 3.6.8 some of them are eventually updated/upgraded, some are redesigned with more functions, so for now, just read and read, and everything will be Ok...