Hey Vern, hopefully I can help out a bit.
First of all if you're going up to 4 miles, you'll want to get a 50 watt radio to handle that distance. Handhelds are great in certain applications, but have limited range. Almost every 50 watt radio we sell is a
Vertex VX2200 mobile radio. We've had great luck with that manufacturer, and trust those radios in even the harshest conditions. As far as radio upgrades are concerned, there's not really anything I would suggest. Our radios are always programmed with over 40 of the most common offroad channels, but if you have any custom ones, we can always program them in for you prior to shipping. It's not really an upgrade, but I would of course suggest getting a harness system that would allow you to transmit over the radio while wearing a helmet. What I would direct you towards is the
single seat offroad harness. It allows you to connect a
wired helmet to the radio, and have a
PTT button on your steering wheel which keys the radio when you hold it down. When it comes to the antenna, we pretty much always suggest a
1/2 wave VHF whip antenna. It's able to be mounted directly to your roof through a small 3/8" hole. This way gives better reception due to the flat metal roof providing what's called a "ground plane". However, if you don't want to mount to your roof, we have antenna mounts that clamp directly to a roll bar. Suggestion: it's always best to mount the antenna to the highest part of your vehicle.
As far as maintenance, when the radio is installed properly, You don't really have to do any maintenance at all. If you have to wash the interior of your vehicle, I would suggest covering the radio with something to stop water from being sprayed directly at it, but other that that the radio simply needs to be turned on, set to the right channel, and you're set.