Yeah, as people have pointed out I'd suggest a slight attitude and accuracy adjustment.
One, you aren't choosing anything in Army officer recruitment, you are competing while at RMAS for limited places in your preferred arm.
Two, there is absolutely nothing wrong with planning to spend 4-5 years in before leaving, it is what the majority of people do. It is, however, not smart to say so openly, for the reasons
@CRmeansCeilingReached said, as well as just plain people skills. "I'm only here until I go do something proper" is occasionally something you hear from Sandhurst cadets or prospective officers. It's not the strongest pitch, is it?
Three, despite what everyone will tell you on here, you can get quite involved in the actual intelligence work. However, bear in mind that your primary responsibilities and job will be other things, and so you will have to balance the two. If you can work hard and fast, and are capable at the intelligence bit (any decent officer should be, it's not magic), then within your own unit of course you can do it. But your first responsibility will be everything else.
Four, like Sandhurst, you submit a preference for what job / unit / battalion you want to join, and then they post you where they want you to go. There may be some coordination between those two things. Often there is not. Mostly what happens is that you say: I would like A. They then say: we only have B available, so put that down as your preference. There is then about a 50% chance that you get B and a 50% chance that you get C. For officers, I'd suggest that at maximum one out of four posts you get is what you actually wanted at the start of the process. That's a lot lower if you want a specific and gucci post (which are obviously the ones that the most people want). Mostly it is a matter of working out what the least unsatisfactory options are from a limited list which doesn't include exactly what you want to do, and hoping you get one of those. That is the system throughout the Army, however.