Is this your first 3D profile?

2-strokes are easier if you're learning to hover -- they torque less than a 4-stroke. They're also easier/cheaper to fix if/when the inevitable happens (don't ask how I know this) :-)

I've got profiles with TT46Pros in them and a couple with Saitos (82 and 100). Once you've mastered the basics, the 4-strokers provide a few benefits but also require a little more skill to take full advantage of -- they're quite sensitive to small throttle movements when hovering or harriering.

Another thing to consider is that the Mojo is a very light aircraft and some folks have had problems with vibration when running big 4-strokes, although I believe the 72 is somewhat less shakey than the 82 or 100 -- but the 82 puts out quite a bit more power (I'm told) so I wouldn't bother with its smaller brother.

You might also want to look at things like the cost of props. An 82 needs a 14x4W or 15x4W (depending on how much nitro you run) and they cost quite a bit more than the 12x4 you'd run on the 2-stroke. If you plan to bust a few props then you'll have to add that cost to your flying bill. I went through a lot of 12x4 props when I was learning to 3D but haven't broken one now for nearly a year.

As for servos -- on a 40-sized Mojo you can get away with standards (S300? or HS425/475) quite easily.

Faster, stronger servos are good -- but you probably won't notice the difference if you're just starting (although you will later). I fly HS5925s on my tail. These are digital, metal-geared and *fast*, real *fast*. On the wings I use Futaba S3010 servos, these are non-digital, nylon-geared and also reasonably fast and strong but I don't like them much because they're too sloppy. With the throws you'll be running for good 3D, even a half a degree of movement or 1/32" of bearing slop in a servo produces a *lot* of unwanted slop in the control surface.

Tell us more about your experience, abilities and budget so we can help more.