From my experience as a pilot recruiter a single side of A4 is enough. Any more and the good bits are hidden and missed. Make it concise, relevant and DO NOT use all that military jargon that is the norm in the services but incomprehendable in the real world !!
Get it looked at by several people before you finalise it. Get your wife/girlfriend/partner to read it and if they are non-military they should understand all you have written easily.
Good luck !!