Int O is Ops Support. Your customer is therefore Ops. On a front line unit it is supporting the commander and providing the intelligence the commander wants. On a sqn it is supporting the aircrew, ensuring that they have all the intel that they need. This is not just the immediate tactical intelligence but the indepth knowledge that they need to 'know their enemy'. In the Cold War this was relatively simple.
Now it could be anyone or anything. The Int O must gather and filter but the filter is where you will fall down. Too much or too little and avoid the secret squirrel syndrome.
Don't dispair of Admin. We knock 'em mercilessly but, like aircrew, they are also being downsized with JPA. The admin wallah is not necessarily desk bound but could also be the man on the ground in charge of force protection. Our 'man in East Timor' was a junior personnel admin officer. He made the national press, sitting in the door of a chopper, SA80 on his knee.
Admin is good for a later career in HR. A law degree is useful. Another good, post-service job is Supply (Logisitics). A science based degree would not come amiss.
For intell I would suggest a history, international relations or humanities degree although science is also useful especially for the tech int guys where Engineering is probably a must.