Share the best tools and strategies for building a mailing list from organic traffic

Hi! I just launched Replicate Codex (https://www.replicatecodex.com/), which is a free tool for people to search through a list of AI models and compare them before building new products.

I want to build our community by increasing the number of signups on the mailing list. Right now, the mailing list is a digest of new and updated Replicate models, curated by me.

For those who have built similar lists, I'm curious:

How did you demonstrate value to get people to sign up?
What tools did you use to maintain the list? Currently I am split between substack and ghost and I'm not sure which to standardize on.

I have gained ~35 subscribers in the first week, so I still have a little time to get this right. But the number is growing daily so I feel the need to get this choice correct.