You're dealing with contracts and licenses. Fishing the internet for opinions that confirm what you want to do is not going to avoid problems.

If it matters, you need to hire a lawyer. Suppose your former employer claims that you acted in bad faith when proposing the MIT license? It doesn't matter if you did or didn't. Your former employer probably has deeper pockets for hiring lawyers.

If you're looking to start a real business, paying lawyers is part of it. This won't hinge on general principles. It will hinge on specifics and the degree of good will involved.

Good luck.