Ive worked pretty extensively on modding the platform behavior from the base plugin and it can do anything you want. there is really no use in making your own because its made for you and its pretty easily built up and modded.
Especially if you don't know how to program jumping there is a good chance it would be hard for you to use concepts such as time delta to make your characters run/Jump/Walk smoothly. You would also need to program a whole separate movement system for your enemies.
As stated Above take a look at the tuts and other caps to see what has been done and can be done with the built in movements there is no need to feel like you have not done anything because there is plenty of other stuff to code.