Do you have a value entered in your home off distance dros in homeing and limits? If not, do you have a work coords that is being called like G54? post your xml and code and I'll have a look.
No, not all buttons are created equal. The jogs need to be functions rather than script if you can. The problem with VB is it is not smart enough to recognize on press and on release. If you get it to move useing the script, how are you going to stop it?
Yes, it will be in the C:/Mach3 folder and will have the .xml file extension. There may be several so be sure to choose the one you use on your machine and when you upload it make sure it has a unique name.
I think there is an example in the SDK and you may also want to watch the videos. With the release of Mach 4 right around the corner you might want to wait.