hi dear Juan,
I tried to have custom MM3.1 by following the instructions presented in setting up development environment for MM2; however, when it comes to "npm install" command, there are some progresses but at the end I'm facing with a error that i can't understand it. I should say i had no problem with MM2 development environment and it worked perfectly as i had many changes in the app.
I'll be glad to receive your comments.
Regards,
Azarmi