Let's start by positing that there's no 'fair' way to do this. Because there's no way to 'fairly' measure each individuals contribution which in turn needs to account for 'people are different'.
You might measure effort in, (aka hours) but not everyone's effort (time) is equal. You might measure value-add, but then nobody wants to do the hard trivial stuff (like docs.)
If it was me I'd likely just have 2 levels, "core" and "casual". With a relatively low barrier to being "core". All cores get the same, all casuals get the same.
Once you stray from "we all matter the same " you invite comparisons etc that will ultimately divide, not foster community.
If you raised enough to have people go full-time I'd add that as a layer above core.
Good luck, and well done on getting the funding.
