I recently built a similar thing for learning purposes using firecracker + the firecracker go api. I wrote a small init system in rust and combined that with filesystem images derived from the Debian, Ubuntu etc. container images (that can be extended with more layers).

What really surprised me the most, is how quick and simple it is to compile the linux kernel. Cloned a tag with --depth 1, configured it and then it took ~ 5 minutes to build vmlinuz.bin. As someone who is too young to have had to regularly do that, I had heard multiple stories of how long that's supposed to take but it really doesn't.

I then tried to move from firecracker to qemu microvms but didn't get that far yet since I didn't have more time.

All in all a great learning experience and if I wasn't an undergrad student with no time, I'd love to build a service/business around it.