GPL is not MIT. If your software is GPL, you can sell it relicensed as MIT for income.
Doesn’t matter. When companies pay for support contracts they don’t care whether the code is GPL or MIT. They care about the support they get.
You can only do this if you own the copyright for all contributions.
Doesn’t matter. When companies pay for support contracts they don’t care whether the code is GPL or MIT. They care about the support they get.