Could be okay, I usually don’t touch servers under $20/month, but I found out that even a Raspberry pi can run Mautic pretty well. You should be okay with couple of thousend emails / day. The question is how many page visits you want to track. If you have a lot, than your Mautic needs to be fast.
SES is not happy about adult content. For Postal, you’d need to understand basic domain administration including reverse DNS, how to handle feedback loops from providers. I suggest you read all the providers you can find and see who is okay with your content.
I think you are better off to look for another source for emailing techniques, there are forums especially for that. This forum also discussed it over and over again, but maybe somewhere it’s better summarized.