Can I install a 200 amp service panel and keep using the 125 amp meter base if I will not be using all of the 200 amps from the service panel? We only installed the 200 amp service panel for future addition.

I think you posted this in the wrong area. But the answer will still be the same. No you can not do that. Before installing a new service box you need to call your power company and let them know. Another thing is if the meter only handles 125 amp then trying to squeeze more past it is a fire hazzard. Also the wiring running to the home has to have ample amperage to handle the load. Most are rated at 100 amp. They leave a little room for extra load and to prevent brown outs.