MadamKing, I will PM you regarding instructors. Marion is certainly very good, and I would stay with her if you are enjoying her lessons. I just know that a lot of people clash considerably with her, and she likes to be right at any cost.
As Spyder said, you're not the only one who has taken a horse from nothing with plans for working it up the levels. Hell, I've had that many horses now that I have purchased purely to learn in myself, different methods of training through various problems. I would LOVE to get to grand prix in the future, but right now, my biggest focus is having a total understanding and ability to execute on any horse I have the chance to ride, the absolutely basics. My current horse is ott as well, I had/have big aspirations for him in dressage, he has been mistaken many a time for a warmblood and he is so honest and willing, that sometimes it is tempting to push that little bit more to play with a few higher movements, as he offers them to me!
I think maybe you are thinking of dressage in the wrong context, which is all too common with not only people starting out in it, but even the ones that ARE riding grand prix. I believe that you may have the mindset that dressage is about all the 'fancy' movements and glamour, I may be wrong, but this is how you have put yourself across on this thread. Instead, try to think of dressage merely as training, with the ultimate goal in that training not being focussed on specific movements, but rather riding a horse that is an absolute pleasure. You want immediate, positive responses in the horse. You don't want to have to work and push and pull to do fancy 'tricks'. Your goal should be to ride in total harmony and ease with your horse, rather than pushing it into the 'tricks'.
I'm assuming this is your first horse also? If so, don't rush! Basics, basics, basics are the key to a good performance, they are the heart of a real dressage horse. Without basics, you have nothing. It should take two years of consistent, solid and correct training to produce a very solid preliminary and novice horse. Prelim and novice are far too often overlooked, people want to get out of them as soon as possible to do the 'fun' stuff, but they are the most important levels of all!
I'm glad you have cooled down now and managed to see where we are coming from in this thread. It is in no way shape or form intended to bash you, merely to inform you and give you a little more direction with a touch of reality. And yes, it IS hard to be told, or given, a different opinion of what you're doing. Particularly when what you're doing isn't working and you think you're doing the right thing.
If you really, desperately want to succeed in dressage, you will need to learn to take on a new attitude, and view every opinion, comment and piece of advice, as helpful, and put it in your 'toolbox'. Collect as much information as you possibly can! Go to different instructors to get different view points and ideas, and when someone recommends that you change what you're doing, listen to them, allow them to explain why they believe this is so, and what you could do differently to improve your performance. Then try their way, if it works better, you've learnt something! And if it makes your ride worse, well then you have another trick up your sleeve that you can try on a different horse, that make react better to that type of training.