GD&T works with most types of fabrication from machining to sheet metal. It gives tolerancing that is better able to produce a good part.

Your tolerancing should be done to the widest tolerances possible. It helps with fabrication and cost. So you determine your critical geometry and that should be your tighter tolerance.

Nowadays, I don’t really have a favorite design software. I have used solidworks, creo, fusion 360, and onshape. Onshape was inexpensive and probably the easiest. Fusion I believe is still free for “enthusiasts”.

I’m not sure what you mean by tolerance adjustments on the moulds? Not sure if you mean material expansion or part tolerancing?

Mechanical engineering requires quite a bit of practice and continuous learning. Just takes time. You have to gain a sense for it.

Thank you for the questions! I am here to help!