There is no fee for renewal of both EAD and AP if you have paid for i-485. If you did not pay for i-485 then you either pay or send renewal package with fee waiver. You will not get combo card if you just send only EAD renewal. Only way you will get combo card if you send both applications together and USCIS approves both together. There are cases where USCIS approves these applications separatly therefore, people do not get combo card.
You do not need to file i-131 if you do not wish to travel.