If I buy a gold pass, will this allow me to buy a first class seat ?

It can be used only for some appointed route. If you but the gold card, you can take first class seat. But on most train there is only 20 seats hold for the pass holder. If they are taken, you need to change to other second class seat. And if the train is full booked, you need to stand in the carriage. Thus, it is not that advisable to buy the pass.