It doesn’t require a separate git repo. e.g. you can have one git repo & package MyStuff for the project, with MyStuff/src/MyStuff.jl for the re-usable parts of the project and MyStuff/scripts/ for scripts. Then your scripts can all just do using MyProject for the re-usable utilities.
(Later on you can always refactor into multiple packages/repos as things develop.)
In general, as soon as you start asking “how should I organize this code” you should be creating one or more packages. Packages are lightweight (need not be registered publicly), and benefit from a lot of tooling (e.g. Revise.jl). See also Best practise: organising code in Julia - #2 by stevengj