The mission editor is very simple compared to other flight mission mission editors.
Creating a delayed spawn is also very easy,
here is a thread describing how this is achieved, really is very simple.
Creating new scripts is tough unless you know c#. But these are not essential or you can just use other peoples' scripts.
What is needed is some decent documentation of features and such like.. this is the one thing that pisses me off, releasing a sim with such poor documentation, after soo many years in development is just crap.