Love that you do this. I have a few enterprise projects that do exactly the same thing (minus the embed in one, just scp and untar). Can’t beat the simplicity.
Regarding the original question we use fiber.io for a few systems and have loved it’s capabilities and performance.
I have never used Jinja/Twig, but I have used handlebars, ERB, JSX and other similar templating systems.
Overall, I find Go's template system to be a bit clunky but it certainly gets the job done. The template system is fairly minimal so it feels mostly like working with HTML, but it gives you a few tools to use.. mainly passing data down the template/sub-templates and the ability to define template functions/helpers. Minimal... but it's all you really need.
I converted my business from Rails 5 to Go about a year ago and the ERB was fairly straight forward to convert to Go's template system.. it felt like I was mostly converting <% .. %> to {{ .. }} and changing <%= render ... %> to {{ template ... }}
My server's binary is more than a server, it can execute one off tasks, etc. For example I can execute the server binary with special arguments, ex "server --task admin-reports" in a cron job.
For the database I use Postgresql with the standard library's database/sql package (using lib/pq as the driver).
For scheduled emails and tasks, I store them in Postgres and I have a task that is run through my server binary every few hours (ex: "server --task scheduled-tasks").
I use embed to embed all assets in the binary itself. "go build" and then "scp" the binary to the production server and "systemctl restart appserver"