I think the ideal would be to add grants to the sustainer toolkit and make all of it part of the Open Collective sponsored sustainer initiative.
Creating perks and campaigns on LibreTime - Open Collective could be a responsibility of the sustainers. OpenProducer would be part of the sustainer collaboration and also reaching out to potential participants for this beta.
This is the main thing the LibreTime maintainers need to figure out. What will help you release 3.0.0 in a timely manner? Will funds enable you to spend more time? Would it help to have another maintainer involved? Ideally, how much combined time per week should be spent on LibreTime development.
I’d recommend a budget for one full-time developer (which could be split between maintainers and contributors) as a goal.
Coming up with the transparent process for allocating funds could be another thing led by the sustainer team.
Does that kinda make sense?