First off, I'm really sorry you haven't found your Phantom yet.
I'll take a shot at your question number 1.
The phantom 's GPS did know where it was until the power from the batteries died - then it forgot. But the GPS Satellites and the internet never had any idea where your Phantom was...
It might be my audio editing background, but I have found Sony's Vegas to be much easier than anything else I've tried. It is also very powerful in terms of the wide range of capabilities it has. It's nice that it can handle 4k video, as well as 3D (stereoscopic) video.
You might consider coating the compass with NeverWet. (See http://www.neverwet.com) sold under the Rustoleum brand at places like Home Depot. Once coated, it won't matter if the compass lands in river water, pool water or salt water, it simply won't get wet.
I can't imagine that the coating...