You don't need a 'hip full' of radios' to cover the modes you desire. The SDS100 you have will do DMR, NXDN and P25 - if you have issues with these modes, then post in the Uniden forums and see if someone there can help. I think C4FM is a Yaesu or Kenwood mode, so you'd need a C4FM radio for that.
As for increasing 'range', a good antenna high up in the air with the right coax is the way to go. Yes the radio's sensitivity and strong signal handling play a role, but don't separate one from the other. The 2 go together, and keep in mind that 'range' is also dependent on frequency as well as any interfering obstructions. As a very general rule, as the frequency goes up, the shorter the signal will travel, obstructions aside.
MIke