you must work with OpenGL to render your graphics, if you want audio, you must work with something like jack or alsa
if you want scripting, lua is a good choice
but it depend's on your needs, the type of game that you want to make with that engine, you want it to be a complete software, or a library, all of those depend's on you
First you should think long and hard what you actually want to accomplish.
Will it be a commercial or open-source, or freeware license.
For what kind of games should the engine be used?
Who is going to use it - newbies or pros?
Do you know enough OOD and OOP already?