My team has to increase revenue by 5x this year. How do I break this down?

This sounds like a really exciting opportunity! Low user churn? Your team is onto something good. Definitely get more marketing and sales help since it's time for that.

Quick caveat: I haven't done this myself but I was actively learning about some of this as I was building my own company this past year.

I'd learn a bit more about growth engineering and growth hacking. Here's a great intro written by Jeff Chang who was a technical leader for growth at Pinterest: Intro to Growth Engineering - Learn How to Prioritize the Right Projects.

Generally, at this stage in the product, the engineering efforts that are high leverage are:

1. Investment in the new user's journey to experiencing the magical moment of your product. This is a shorter term investment.
2. Finding a new user pain in an adjacent domain and building prototypes for it with some percentage of your time. This would be a longer term investment and would require knowing your users well.

1. As an engineer, how can I break this “revenue” goal down to help figure out the team’s strategy and what we should be building?

Revenue should be convertible to number of users, and from there, you should be able to infer from other adjacent sources of traffic (e.g. web searches, email marketing, neighboring related features, etc.) how you can fill them and what you can do before solely relying on marketing and sales.

1. Are there sub metrics I should be setting sub goals for?
2. How do I estimate how much ARR a feature will get us? (Or is that just a waste of time because they’re just educated guesses?)

Generally, I like measuring retention using cohorts to see how we're doing on a periodic basis, say monthly. Feature sets change over time, and it's good to understand how retention is changing as new features are launched.

Sub metrics wise, I think the road to the moment of magic will be worth measuring. How many new users are dropping off before they hit the magic? Where at?

1. How do I know if features on our user feedback boards will help get us new customers (and therefore more ARR) vs just making existing customers happier? Our churn has been very low so as nice as it’d be to just build what our existing users want, I want to prioritize new customers to avoid the project being shut down prematurely.

If I could, I'd go talk to them. Ask them to prioritize their problems in the problem space your product is solving. If you can't do this, I'd at least get a feel through a survey. Here's a classic video by Eric Migicovsky (Founder of Pebble) on How to Talk to Users. This might be done through a product manager or marketing lead.

This is kind of a cop-out answer, but the 80/20 rule for increasing revenue is actually very simple: just raise prices.

The guy from ProfitWell has a good framework around it. In particular, on the product side, can you add steps in the onboarding to determine how much value a user may get, and then offer them custom pricing?