Hi ariel,
I'm glad those suggestions were helpful. As for height on the bench, here is the best starting point: Have forearms parallel to the floor with wrists extended neutrally and naturally, and your elbows either level with the keyboard or no more than an inch lower. If you try that, but it's not quite you, then use that height as the baseline to further adjust the bench height to your preferred comfort level. At that level, gravity should assist you with relaxed arm weight for richness of tone, but if you're too low, gravity will work against you, as you'll have to use more effort in lifting the arms; however, if you're too high, you'll produce more of a dry and brittle sound. Plus there'll be an up-flex in your wrists which over time could cause problems. Once decided, you will then automatically be able to get it right on stage every time. You might want to discuss this with your teacher too.
By the way, I notice that you handle tension in the shoulders (that is, when they tend creep higher as you play difficult figuration). You've have an inner voice reminding you to lower them to avoid discomfort. You manage that bane of pianists extremely well, which helps to maintain a relaxed playing apparatus at all times. Good!
Ax is one of the best artists for playing Brahms that you could have picked. Practice and persistence are important, but inspiration goes a long way too!
You'll do well in Paris, I'm sure. Good luck!
David