I've never owned a 4wd before and to be honest know buggar all about them. What I have learnt in the last few days is they cost a heck of a lot more than I was thought

I brought a boat a couple of years back and have been towing it round Otago behind my 2L Nissan Cerfiro but really need a little more power for towing it.
I'm not looking at getting into major off roading at all, just wanting to use it for towing the boat to central Otago and able to launch it off the lake side or off the beach occasionally when the surf is flat. I will also use it for towing fire wood short distances as well
It would be also handy for getting into valleys like the Ahuriri valley where the road can often be washed out and very difficult to access in a 2 wheel drive car.
I do a bit of hunting as well so it will be out of town on a regular basis.
I'm wanting to buy a double cab ute with a canopy and have a budget of $15000-$18000 and not sure of makes or models to look at. I have been looking on TM and there are a few tidy looking Mitsubishi Triton's on there with reasonable km's around the 2003-04 area, Nissan Navara's (I like the look of these) as well, a little older and higher km's in my price range. The Toyota hilux's seem to be a heck of a lot dearer around the early 2000 models with very high kms on most of them but I hear they last forever. Mazdas, Fords, Holdens....there are a few choices.
Petrol or diesel, auto or manual? Does one have an advantage over the other for the type of use I have mentioned?
Any advise would be greatly appreciated on what I should be looking for or what to avoid. As I said I'm a total newbie to the 4wd scene and there just seems to be so many choices its a bit over whelming where to start.
Cheers
Steve