Realisticly, to be able to fish 4 in a boat, it has to be a fairly large boat, 18+ at the very least, even that would be cramp for a cuddy boat.
Once you have chosen the style/size of boat, then you have to decide what your budget is, is it going to be a new boat or a second hand, or even a sound but much older boat.
If it's a 2nd hand boat, you don't have much choice on outboard. You can only choose from what is available at the time you are looking. However, I would avoid old 2 stroke, if fuel consumption is your main criteria. On the other hand they are easy to work on if you are planning to do the maintenence yourself. 4 Strokes are more economical by do require a little more maintenence than 2's.
Have a look at Dave's website, he's got some boat and outboard on reviews by their owners. It also contains lots of info on must have in a boat.
Dave's Website