Yes, you are right - Donation doesn't help that much. When platforms like Open Collective and Pateron, maintainer doesn't earn that much unless big players are convinced.
In my repo, I don't have dual licence system and paid corporate versions.
What type of support can be provided? This seems nice idea
You alone probably cannot offer support. It usually means enterprise support, search for MariaDB or MongoDB services and see what they are doing.
The bottom line is that, in order for the big companies to use your product, you have to offer support to it, in any environment/timezone, and to all your product dependencies (example if it uses a database you have to to that as well, or have a collaboration with another company).
I say "big", because if someone is "small" probably will not have the money to pay for a support.
You can find many resources on this field, this is one of them I actually attended Open source slush by one of the MySQL and MariaDB founders.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.