1) could I add Wifi to this? Is it cheap and easy to do, both in terms of hardware and software?
There is a roughly inverse relationship between cost and ease here. If you pay upwards of $80, you can get a nice, easy to use break-out board or shield that you can hack together with a FLORA to get WiFi going. If you really know what you're doing, you can probably get the cost down to $20 or less for the WiFi interface, but its not going to be fun for a beginner.
2) what about RFID?
Similar story as for the WiFi, but RFID does use cheaper tech than WiFi.
In general, any protocol-based technology that you want to play with (Bluetooth, GPS, WiFi, RFID, etc) will more or less require that you understand a certain amount of fundamental knowledge of electronics. Once you're feeling comfortable with the Arduino platform as a microcontroller dev platform (not just a fun toy), then doing more complicated projects like this will become more trivial.
Some people prefer to learn by doing, and will have no problem dropping a good amount of cash on buying many parts, but you're going to need to keep your head up; you will hit many brick walls and dead ends, and you will have to find a way to keep yourself motivated through the process. It's just my personal recommendation that if you have the time, start small and work on projects that are at your skill level (get an LED to blink, then get several LEDs to blink, then use a button to control them, etc.). Good luck!