Carefully curate and vet both devs and mods. Fight hard to ensure that the character of development and moderation does not depend on just one or two people, but of active internal practices that recruit, support, and otherwise churn out cool people that support the mission and guard it from people who don’t get it or are aggressively hostile towards it. Shoot for 2X of what you need (devs, mods) and start getting worried if it dips below that.

Ensure that funding models for hosting and development work are limited but viable. Make a rejection of certain funding models a hard requirement of being a dev or mod. Everyone thinks they can resist corporate pressure, but if you, for example, make a site ad-dependent, you will eventually come to the conclusion that you need to make editorial changes to avoid losing advertisers, and have a very good chance of falling into false dichotomous thinking: either the site dies or we ban X group that makes our site less attractive for advertisers. Trying to find ways to profit off of Reddit is why the APIs are basically planned for demolition right now. This also has a dev implication: optimize for lightweight resource use. Obviously devs try to do this in general, but you’d want to make it a real priority, as cheaper server (and dev) costs are a better way to make the project viable than finding more income.

Keep to your political commitments and ban/exclude those who stand for their antithesis. Those people already have corporations on their side and there’s no point to putting in all of this effort to just end up being a Reddit clone full of the incurious and bigoted. I’m sure you already know this, but lax moderation against, e.g., right wingers tends to create spaces where they want to be and nobody else does.