You can use nix alongside guix, it'll just double-up the dependencies on disk:

services (append (list (service nix-service-type))
                    %base-services)))

Services are, in guix terms, any configuration change to a computer, so creating your own service 99% of the time is just extending etc-service-type and creating a variable interface to fill in the config file text yourself

Creating a service as in a daemon of some kind uses shepherd and involves extending shepherd-service-type or home-shepherd-service-type with your service description, depending on whether the service runs in root or user space.

Shepherd service configurations aren't actually part of the guix spec(https://www.gnu.org/software/shepherd/manual/shepherd.html#Defining-Services), but still use Guile, so you can interoperate them super easily.

It's important in guix to understand lisp pretty thoroughly, and knowing how to program lisp is still a very useful skill to have so I'd recommend learning it even if you never touch guix.