Maximum Tune Japanese Wiki
Incredible resource for anything and everything WMMT which is constantly updated. The only downside is that it's entirely Japanese, but direct google translation is ok for most basic info. We get a lot of our info from here.
Here is a list of MT resources that I personally use and recommend:
SOARS Team:
A South Korean based group who make video content of battles, story mode, time attacks, and MT experiments. They usually have most of their content in both Korean and English. Highly recommended.
FKNSRS (Akuma) YouTube Channel:
Active contributor to MT.org. Lots of battle videos new and old. Home also to possibly the only English brake blocking video tutorial.
Wangan Midnight Expressway Forums:
Community base for most international regions. Some good legacy info but mostly for discussion and Q&A.