Personally If I were going to buy a new radio today it would be a Galaxy 959 or 949, or a Uniden 78 Elite. If you arent into SSB, dont buy the 959, and If you are only planning on using it for wheeling you could even go with a Uniden 68 Elite. Most of the Uniden line are great radios, even the Uniden 510 can be made into a talker.
4 watts is the legal limit. However many people run much much more than that, but its not in your best interest. If you want to run lots of wattage get your Ham ticket and you can legally run lots of power.
A lot of wheelers run the Cobra 75? its the model with all the controls in the mic. I personally am not a fan of this radio just because CBing is a hobby of mine, I dont just use it while wheeling. Also, If you are looking at the Cobra radios, be aware that the "sound tracker" models are known to have a lot of problems. Also know that the new Cobra 148 is NOT the same talker the old discontinued 148 was.
Stay away from radio shack coax. Get some good (belden) RG-8x (AKA mini-8), and use soldered on Amphenol connectors.
The biggest thing to remember is to get a good antenna. A crappy radio and a good antenna will out talk a good radio with a crappy antenna any day of the week. A lot of wheelers like the Firestik line of antennas, which are fine on the trail, but they dont get out too far in my expirence. My favorite antennas are the Radio Shack 102" SS whip, and the Predator 10K single coil (I wouldnt recommend the predator on the trail though.)
Also, if you are going to drop the coin for a new radio, buy a SWR meter also. The SWR meters that are build in to radios are notoriously inaccurate. The radioshack model is fine.
Any other questions just ask.