customization can be a beast - my recommendation is to get someone who's not a beginner any more, or put this requirement on the backburner while you collecting experience in your project.
The solution on the data side (no two overlapping events) would be relatively trivial, but you probably want to give a nice UI for this as well, instead of just ignoring the input. Thus it'd be backend AND frontend code that both must be customized. Some technical details can be found if you're searching for "a plugin to extend a plugin". Alternatively get the sourcecode and see if you can utilize it. If it's too complex: Continue in my first paragraph.
