Questions on migrating to an nGauge and releveraging my SCT x3 for another vehicle

All, I have a few questions.
1) Will an nGauge work with a 2007 GT500?
2) Will an old SCT x3 work on a 2015 F150? Assume it will but wanted to make sure?
3) I have a 2007 GT500 that I used the SCT x3 on and want to do the following, factory the GT500 via current SCT x3, use the SCT x3 on the F150 to flash and then use the nGauge for the GT500 and also use as a gauge after flash.
4) NET NET can I use a existing tune from a GT500 and get it on nGauge and then load to GT500
5) Who makes the best tunes for F150? I am just looking to get a 87 and 91 octane tune for tow only (truck will be used only for trailer/tow). Looking at MPT and 5 Star Tuning.
6) Why do I have to pay more for nGauge tunes? Credits?