Last time i checked, IE9+ are still supported browsers. Of which, IE9 has no support for Flexbox and IE10+, only have partial support.
(Not counting Edge on those stats as it is after all an entirely new browser).
Agree 100%. My boss has invested in Treehouse to improve code practice. We also started pair programming to help each other identify potential bugs and teach each other new ways of doing things. It reduces tech debt as well.