Hello OP, I haven't read all the comments in this thread, please forgive me if I duplicate someone else's ideas:
First off, I really like what you've done so far, this is fantastic and I dig the idea despite some of the potential payout exploits that you'll need to guard against.
My suggestion is to find the moderators who have wishlists of features that they want reddit to implement. Don't try and entice them onto your platform, just ask them for advice on what features the moderation tools should have. Implement those tools and ask for feedback. Places like AskHistorians, AskScience, gonewild, and other specialist subject subreddits will all have very specific requirements for their mod tools. If you can support those requirements, or at least make it so that it's easy for someone else to build those tools, then I think you'll have a headstart over others.
A couple of other items:
reddit has edited user's comments in the database before. Perhaps consider implementing public key signing of comments on the backend, such that once a comment is made, it can be verified. Hide the gory details from the users unless they're a power user and want to see that stuff. Being able to say "I wrote this and it hasn't been modified", well that's pretty powerful in my opinion.
Allow users to set their profiles such that when someone buys gold for them or otherwise rewards them, the money is instead donated to a charity of their choice. Said charity can be displayed in their profile, comments, or neither.
Talk to lots of people, watch how they use reddit and other sites that include moderation, learn from what they say. Mods are going to be an important customer for you, they manage the communities that will create content and draw people in.
Decide very early on what your personal values are and what the values of the site are. Not in a corporate useless bullshit kind of way, but instead to clearly state what people should expect. Decide what rules mods must follow vs those that are optional. Same for users. Transparency and clear open communication is something people are really missing right now.
Allow people to display the site in multiple different ways that suit them. For example I use ublock origin rules to display hackernews comments no wider than about 8 to 10 words. Some people like old.reddit.com, others hate it. Give people options and make it easy to switch between them.
Allow people to not see advertising if they don't want to, as long as those costs are covered via a subscription (which you seem to be doing, nice!)
If you haven't already, implement a rich text github markdown text entry widget.
Don't bait and switch.
I'm looking forward to seeing your progress, I hope you succeed and that I'm using your site in 5 years! Good luck!
EDIT: I also wanted to add, make your site as fast as hackernews. Can you load the text first, then the rest of the stuff, without reflowing and shifting content around? Speed keeps the site feeling snappy and doesn't "punish" people for clicking discussion links etc.