Hey,
if this works for you just fine then there is not much to worry about. Consider either freezing firmware via armbian-config or create a backup of your OS before doing major updates like kernel since those nightly images feed themselves from the beta repository.
Anyway you are free to build your own image using the build framework. Check the documentation, for standard images there isn't much to it.
https://docs.armbian.com/Developer-Guide_Build-Preparation/
https://docs.armbian.com/Developer-Guide_Welcome/
In terms of kernel choice there isn't a perfect solution yet. Both legacy and vendor are, as their names imply, aged vendor bsp kernels which support most board functions but on the downside won't receive much attention in future. On the other hand there is edge which follows mainline as close as possible but is under heavy development to add missing board features and until completion, if this state is ever reached anyways, will take years at least. Basic functionality is there and its mostly fine for server tasks.