1) Not critical that the mid-sole line on the ski and boot match, good place to start but not critical.
2) 5mm could make a bit of a difference, but then again maybe not.
3) Being foreword could possibly help.
So here's the deal! You have a pair of demo bindings, and you can now adjust your position on the ski to you re liking. )BTW Lou has some great info on this). It really hark-ens back to the day when we tried to install the bindings so that the ball of foot (BOF) was within a bout a CM of the running surface of the ski.
Put skis on a flat surface de-camber ski by pressing down on the middle of the ski.
Make a mark on the side of the ski where the contact begins with your flat surface at the tip and at the tail.
Measure the distance between the two marks and mark a mark in the middle.
With you re ski boots on take a hammer and tap the medial side of the shell where the ball of your foot would most likely be and make a mark on the boot shell.
Align the new mark on your boot with the middle of the running surface of your ski and start out there. I am betting that you will find that this will put you very close to the sweet spot for your boot and ski combo.
The beauty of the demo set up is that you can move it forward or back.
Again, Lou does a great job of explaining all this. Nothing has really changed for setting up skis, in the last 30 or 40 years except for the ASTM/DIN mid-sole mounting point, and that was introduced to limit screw pull-out and the positioning of binding mounting plates etc. With some of the new Funny Skis we may see a change, but that remains to be seen.
As far as setting the correct forward pressure, leave it up to the certified technicians.