In an ideal world, you'd get a couple of Tunze 6100's and a Multicontroller - but spending close to four figures is most likely out of your budget . . .
Seio pros: moves more water in a greater area (although with the nozzle mod on the Maxijet this advantage is lessened a bit)
Maxijet pros: somewhat cheaper, takes up less space in the tank, uses less electricity (therefore generates less heat), seem to do better on wavemakers than Seios which sometimes have trouble starting up again.
The most important thing from corals point of view is water flow. The choice is yours.
The standard placement is one at either side of the tank towards the back pointed not directly at each other, but at the same spot (usually the centre front of the tank) - so that the two flows collide and create random currents throughout the tank.
I wouldn't bother with "live sand". Cheapo playsand will become "live" anyway by itself in a few months from the live rock. You should also be careful about mixing different types of sand. Overtime, the smaller grains will work their way down to the bottom eventually creating two separate zones. This will affect nitrification processes and may disrupt the operation of the DSB.