The G4 is a great radio. (I have one) However, you likely will not be able to "scan" all the counties at the same time. It is possible to add the programming. Do you have PPS software installed on a computer? If so what version?
Do you know specifically what talk groups (Law, Fire, schools Local Govt, etc) and MARCS site you what/need?
Preble Co is not too bad, it only has ~24TG's. However, Montgomery Co has a ton of TG's to pick from.