There is already an option of Tagging Mods, Styles etc. When you open any addon thread you will notice a list of options on the top right hand side. You can find the tag option there (Underneath "Mod Information")
As for the Chatbox, I haven't used any. I would recommend this chat plugin though;
https://vborg.vbsupport.ru/showthread.php?t=267506
Take note that is isn't supported as it's in the initial stage.