One question...

Theme: Pad, soldering point, via, plated-through hole

How can I gold plate pads? E.g. for buttons or for a slot connector?
You have to discuss this with your PCB manufacturer. You can create slices over all buttons (i.e. filled circles) in the "Gold top" layer. Or a filled rectangle over all pads of a slot connector at the board edge, twice top and bottom.

You write to your PCB manufacturer that you want gold plating there on the pads. The areas can later be exported normally to an XGerber file.

Here comes an example for only copper top:

1 (Fig. 1: Gold-plated contacts on the lower edge of the PCB)

Thick conductor tracks or rectangular SMD pads in the upper copper layer (blue, layer 16). The solder mask is hatched green as a rectangle (layer 18) and the gold plating is hatched brown (layer 17). Both rectangles are drawn completely over all pads.

Repeat the same for copper bottom on layers 2="Copper bottom", 3="Gold bottom" and 4="Solder mask bottom".