No you don't need a air filter, but some use a piece of Womans Nylon Stocking with a O-ring, and they slide it over the Carb. It doesn't effect the power of the motor... and it does keep the bugs out.
You fuel your plane by disconnecting the fuel line from the carb. It's the same line that runs to your fuel tank. Disconnect the line connected to your muffler... when the fuel runs out of the line attatched to your muffler, then you know your tank is full. Re-connect everything and you are good to go. Welcome to our hobby. Hope you have a flight instructor... It will make your plane last longer.
Luftwaffe Oberst
Radio Aero Modelers Club
AMA District II
Pulaski, NY