This is great and very happy to see it. Mailchimp is annoyingly expensive for what it is.
With that said the sending of the emails is the easy part. Deliverability is hard.
Sending via SES is pretty likely to go straight to spam folders or worse. Granted if it’s 100% opt-in and you have the kind of audience that will hunt for the email and mark it as valid you’ll probably improve and be ok long term but it’s something to think about.