The biggest question you need to answer at the beginning is if you primarily care about a getting a game done, or just want to play with writing game technology

The biggest question you need to answer at the beginning is if you primarily care about a getting a game done, or just want to play with writing game technology (graphics etc.), while maybe ending up with a finished game in the process. For the former case, you're always better off with an engine (the exception being simple 2d titles), while in the latter you obviously write everything from scratch.