I use a medtronic 5230 G with an enlite CGM system, You would want to get a dexcomm CGM if you were going to do this. As for separating a dexcom from a pump, we do have at leas tone member who has done this and he feels it has been beneficial to him. I imagine there are more I just do not know them.
As for the benefits? I do feel that combining the two devices is likely best. the reason I say this is because a pump allows for instant fine adjustments in dosing. Injections are far more long term in nature. If you think of it when you take insulin you are committing to eat a certain amount usually well before the true active period of the insulin. With a pump the two actions are pretty close together. You eat you dose only for the amount you are eating. In essence with a pump you inject based on what you have eaten. When you use MDI ( multiple daily injections) You basically eat to your injections. It is a very big difference.
I used MDI for 28 years and I did not want to get a pump. At this point now after 10 years of using a pump I woudl never go back. They are just so much better for me.
Still one method is not necessarily that much better than the other. If you are willing to take more injections it is more a matter of preference.
I wish I had done it earlier. as for the CGM? A dexcom will give you information you cannot necessarily use while doing MDI. Again it takes longer to act and you get stuck having taken more insulin than you wish to to eat for. I find the convenience of the pump absolutely incredible.
I wish you the very best.