I would recommend wait. I have bought domains thinking they were awesome only to realize a couple of weeks later that the domain actually sucked. As your idea matures also the naming will do, no rush to buy anything when you are just excited about the next "big" idea you had.
First decide if you intend to pursue the online business idea. Before purchasing the domain name it makes sense to examine the domain names of rivals and industry leaders. Then take note of any keywords they use as well as their domain extension.