having said that Imay be able to power the receiver with a separate battery pack of AA-anyone with any advice on this would be appreciated.
It is certainly possible. The receivers usually have a range of voltages from 3 - 5V so a couple of AA batteries would power it but you do have to ensure each of the ESCs plugged in aren't powering it either (so cutting the +ve/red wire would do). Wherever that passes failsafe is another matter.

I was looking at single ESC's but if I put 2 single ESC's in-will I have to use Tank steering or is there a way to run them off one stick without a clash -ie when I go forward and also left or right it will be getting a negative and positive voltage to the motors at the same time-won't it?.
Most modern transmitters can do this via elevon mixing, depending on what your transmitter is. On the DX6i I have, it is Menu > Mix 1 > Ele to Ali. On the OrangeTX types, it is Menu > Model Setup > Elevon. You can also get a hardware based V-Tail mixer which does the same thing if your transmitter doesn't support it but in my experience, they don't hold up very well.