measuring my EX-1, you'll need veneer that can cover an area of at least 600mm x 480mm.
If you go with bookmatched veneer, then the overall size of two pieces must be greater than the above. Because of the body shape you could slide one piece forward and one back (as long as the overall width was wide enough), but then you'd lose the bookmatch effect and it would look really odd.
Your first link has veneer that is just two small (the picture show two sheets of veneer, so is only 360mm wide overall and 500mm isn't long enough).
The second one is a possibility f you had two pieces joining along the centreline of the guitar (with the join running through the middle of the pickup routs). The straighter the grain, the better it would look. What would look odd is if the grain was going off in different directions on the two pieces of veneer. You 'd have some ability to cut the veneer at an angle so that it lined up as best it could.
The third one will again be too small.
So the second veneer is the only one that really works at all, but how well it could work will all depend on the actual pieces you get and how straight the overall grain is. The straighter it is, the more like a korina Explorer it will look.
You could always ask them to pick the pieces with the straightest grain, or even send you photos of what they have so you can select the pieces.
Yes, it would do for the back as well.
The body's flat, so its easy enough to just glue the veneer to it. One half at a time. You'll need quite a few clamps and a nice flat bit of wood to act as a press.
You'll need to be careful to avoid getting any glue on the face of the veneer, so be quick and wipe off any excess glue that squeezes out with a damp cloth.
Once you've glued one piece of veneer on, then you can trim the excess veneer with a sharp knife, using the sides of the body as a guide.
Then stick the second piece of veneer on and repeat the process. You'll need to ensure that you don't get any glue squeezing out along the centreline that doesn't get wiped away, so only apply a very thin layer of glue, and leave the very edge of the second bit of veneer uncovered by the clamping board, so that you can just see the join to wipe it, and can ensure that the two bits of veneer are tight against each other with no gap.
I'd also make a paper template of the body shape before putting any veneer on, and mark the pickup routs and other holes on it, so that it's then easy to know where the holes are to then cut away the veneer over the holes with a sharp knife.