I suggest focusing on making the project work great with the given sensors first. That's actually a very challenging problem! Once it works *great* with the given sensors, if you have time, money, and energy left over, feel free to add whatever fancy bells and whistles you want. (A robot arm that can scratch your back? An airsoft gun that can scare away squirrels? A large 16x16 LED display that animates a face? Who knows?)
Chances are, you won't actually have any time left over, and you should actually be spending all your time on making the original project *great*, so starting with that is good project management :-)