Would you like to see more regulation on this community?

Unless there are people downvoting every post or similar, no. "A community to discuss anything related to veganism" has room for all sorts of posts and discussions. Carnist trolls currently seem to be few and far between, so current moderation practices are working.

What rules should be applied?

That depends on the direction that everyone wants the community to take. @HubertManne makes a compelling point about splitting a community like this into a vegans-only community and an outreach community, in which case each would have different rules. For now, this seems like a community open to everyone engaging in a respectful way, so the instance-wide rules should suffice. The site's wiki even states:

A solarpunk culture would strive to dissolve every form of social hierarchy and domination – whether based on class, race, gender, sexuality, ability, or species – dispersing the power some individuals or groups wield over others and thus increasing the aggregate freedom of all; empowering the disempowered and including the excluded. It is rooted in the legacy of such liberatory movements as anti-authoritarian socialism, feminism, racial justice, queer and trans liberation, disability struggles, animal liberation, and digital freedom projects.

What would you specifically not like to see?

I would not like to see posts removed or users banned for

• disagreeing with or questioning a popular narrative;
• linking to external sites/articles that relate to vegan living, animal liberation, or the struggles of particular non-human beings;
• expressing Yourofsky-esque misanthropy;
• criticising people (including other vegans) who engage in oppressive practices;
• exercising free speech in general, so long as it does not consist of personal attacks, harmful misinformation, or calls to violence against peaceful beings;
• anything that does not violate the instance rules or the spirit of Solarpunk;
• posting in a language other than english.

That said, if someone makes a post saying that it's okay to eat oysters, I would prefer that the mod(s) err on the side of caution regarding bivalve sentience and ban that user for inciting violence. "Better that ten inanimates go free than that one sentient be eaten" or something like that.