How any other open source is funded (e.g. corporate/individual donations, grants, crowdsourcing, support, ancillary products, etc). I don't believe, at least for an MVP, that much funding is needed compared the scope of some of the successfully funded open source projects that exist.
> Most importantly, why would users care about decentralized vs centralized?
They wouldn't. And ideally, beyond the annoying hoops on initial versions (e.g. discovery/identity), they shouldn't. Your software needs to win on features. A self-hosted, subscribable Reddit clone w/ chat would be a very good start.