What are some good websites that I go to get help with Mutants and Masterminds besides the main Mutant and Mastermind forums on the Green Ronin website?
To be honest the forums you'd probably get the best support questions from would probably be rpg.net. You could sneak in through the back door, post some questions, and as long as you play along with the sites ever shifting terms of service than you might be alright. Back in the 2e days of MnM Green Ronin had an amazing Mutants and Masterminds forums, but that's no longer available.
Have you tried www.echoesofthemultiverse.com? IIRC, it's where the GR fourm users went after GR shut down their original forums. I'm not sure how much traffic it gets.
You can start here. All the rules for 3e Mutants & Masterminds; free.
https://www.d20herosrd.com/
Also, here's the archive of the old boards with lots of player built conversions of comic heroes into the system.
https://web.archive.org/web/20140625112009/http://atomicthinktank.com/viewforum.php?f=23