There's actually nothing wrong with appaloosas, though I'm not a fan of them.
As your in the UK (near me!) it is most likely the color appaloosa rather than the breed. So essentially, it will probably be the same as any other horse ;)
My problem with this horse would be that it is being broken in very, very late.
I usually start the breaking in process at 2 and a half, or 3. The problem with breaking a 7 year old in, is that they have had their freedom for so long, that they are going to put up one hell of a fight. I broke in a 5 year old recently, (I did it for a friend) and it was a hell of a lot harder to break than a 2 and a 1/2 or 3 year old. Most horses, broken at 3, are going well by the age of 6, and are in their prime, but this one won't be going well until 10, or 11. Maybe even later, as older horses don't learn quite as quick as the younger ones.
Then again, I might have just typed that for nothing when you tell me that you aren't planning to break the horse in.