Is another shielded wire necessary for 2nd VR?
 

Quick basic question:
Should I run another shielded wire going to the CAS for the 2nd trigger when adding the 2nd VR conditioner? A quick yes or no would be great.

Yes, and if you want I can send you like 10 foot of special wire i got (had to buy it in 100 foot spool and will never use it all myself) just PM me your address and i'll send it out! I have no noise in my signal.

If you still have the stock front body harness hooked up to your car you can just use that as you CAS wires. Both run through the same sheilded wire.

Otherwise yes you will need 2 sheilded wires.

Yes, yes and YES! All the CAS wires must absolutely be shielded. The shield needs to be grounded at one end only (ECU end...). I go a step further and run it in a different harness then the rest.

Generally the cable I use is double shielded 4 conductor microphone cable with a current drain, made by Beldan. Shielded twisted pair is also acceptable. DigiKey sells some excellent triple shield cable that has a master wire braid shield, then 4 little coaxial cables inside.

What wire gauge is best for the CAS, assuming a shorter run from the CAS to the MegaSquirt?

Wire gauge is unimportant as very little current passes. 20 gauge or thinner is fine as shielded cable in those gauges is easy to find. The only thing you want to watch for is to not make the wires so thin that they are physically fragile.