You are correct that CB is limited to 5 watts. But I think even the handhelds are 5 watts these days as well. For a given antenna, I think you would get similar performance from a mobile or handheld radio. I’m not sure you would get much benefit from front and rear antennas. The 108 inch whip antenna might be best, but a mag mount on top would also be a good choice.
If you want a little more punch, you could get a GMRS radio. It requires a license, but no test and the license is good for the whole family. I think the limit for GMRS is 50 watts.
Of course amateur radio will give you the most options, but that requires taking a test.