As you suspected earlier, you can only add additional keys if you have two working keys to begin with.
2 options for OP: dealer programming & cloning.
A PATS key has a unique RF ID signature. Buy a new key at the dealership and the dealer programs the vehicle to allow the new key's RF ID. My 2008 Expedition can have a maximum of 8 uniquely coded keys (but only 6 remote fobs, go figure). Benefit here is if you lose or have a key stolen, the dealer can remove it from the security module & that lost key won't be able to start the vehicle. For the key and programming, expect to spend upwards of $150 - $200. Get it done during an oil change or other routine maintenance and likely you'll pay less.
Cloning is just that. You have only one key, a Locksmith captures its RF ID and clones additional new keys to mimic that RF ID. You can have an endless number of cloned keys. Pros and cons to both.
Remote control costs vary - Depends on remote start or not, power liftgate or not - which remote you need determines cost - 3, 4, or 5 buttons, remote integrated into key head or a separate FOB. With a keypad on the door, do you really need another remote just to go with the spare key?
I'd personally avoid the ebay/amazon cheap keys and remote fobs due to the huge amount of Chinese knock-offs. I have a Chinese ebay remote that has about a 3 foot range with a new battery. My OEM Motorcraft remote works from inside my pocket from 25 feet away.