Well a fuel pressure gauge would be a good start, and you'll certainly want one if you upgrade injectors. Some guys can run 190's and have no issues with fuel, others have issues on stock injectors and a hot tune, so you really need the gauge to know for sure.
As for injector size... well that's up to you. You could certainly get 155's and do light towing and daily driving without issues. You could go higher too if you wanted. I would plan on doing a fuel system though anyways.