You won't be powering LEDs from your Arduino, and you've made no mention of what your power source is going to be. The Arduino running on 5V is then hardly relevant.
Still not sure what your actual goal is. Are you adding IR functionality to those devices, or are you trying to control devices that you already know use 38kHz IR?
If you are trying to add functionality, RF is a better option. If you have an AC unit already, it probably does use RF and not IR.
So if I play along and just assume you know what you want, and what you want is to flash 6 IR LEDs, then you can start by figuring out how much current you want each of them to see and explain how you'll provide that current. The part with the Arduino is cake. It's just diddling the base pins. But you will want transistors that can handle whatever current you decide to go with.