I am building this audio amplifier circuit, but they have built the PCB using EasyEDA software. If I get the Gerber file from EasyEDA and upload it to your website, will it work??

I want 50 PCBs and this is my first order so I get $20 discount, right?

Also as you are advertising, if take part in your contest you will give $10 coupon, so will I get total $30 coupon??

last question is, coupon can be used for shipping charges??