Start with build environment. There are threads in this section - slightly outdated, but on the other hand environment problem solving is
slightly easier than actual later work.
After that try to build something from either unified branch on HG or dev on @names_are_hard GitHub clone. If it works, you have a working development env.
And if you go git, you can check on your 700D if our recent changes didn't break anything for Digic 5

Later I would suggest playing with minimal/hello-world (dev branch on git, digic6-dumper on hg). This is just a code execution on camera, without any real magic lantern code running. Source code built there is pretty simple - there's whole "startup sequence" there (where ML hijacks Canon stuff) and then just a simple task is started that is able to draw on screen and blink a led.
And you don't need to search for any stubs as 700D is already supported camera

There's a startup sequence flow chart in some thread on the forum, I forgot which.
As long as you don't poke into memory addresses that you are unsure of, you are relatively safe to play with almost any C code there (in fact, minimal build was a base for doom port on 200D).
In the meantime you can join our Discord - we will be more than happy to answer any technical questions.