One thing that’ll need serious consideration:

I feel like it’s inevitable that Lemmy will get an advertisement module that admins can enable. Alternative monetisation methods can also work, such as subscriptions. But users will have to realise that servers aren’t free.

If you’re an admin for a small community and are willing to carry the burden: great. If you’re hosting a community that can support itself by donations: also great. But sooner or later we’ll need some ways to make servers sustainable.

(Not a fan of advertisements and would prefer to be a paying user, but as Lemmy takes off we shouldn’t look down on admins trying to mitigate their expenses).

I don't understand why people think it's necessary. Does Firefox display ads? Blender? GNU/Linux operating system? VLC video player?

No offense, but I think maybe you are so used to corporations trying to drain your money that you don't notice how much amazing software we are using that was built for free. And this software is often better than the commercial competition (for example it took Microsoft 10-15 years to add workspaces to Windows and tabs to file explorer after they were added in GNU/Linux and it took them over 20 years to add a package manager).

Not only was that software made for free, but it also gives users freedom unlike (usually) the commercial alternatives.