Personnaly, I would try to respect the budget I wanted to put in my purchase and what I feel I can afford without feelind bad. If you think you can have any regrets by purchasing too much, just don't and think about your future house and car. Just as you said, you don't want to feel pressured to sell something. Hold on to that thought.
When I go to a different country, especially one where there's options I can't have in my hometown, I go for that first. I try to make the perfect choice between what's the hardest to get and what I would wear the most so I don't have any regrets. Even if I know how some items are a goal in my mind, if I won't wear those that often, I just pass. If what I purchased seems usefull in a daily basis, I know it won't feel like a bad choice in the end.
If I can make any more advice, even if you don't have any Hermès appointment, try to get one on the boutique after purchasing your shalw by asking nicely if there's someone free to show you bags. I love the Sèvre boutique, SA are just nicer there than in any other places in Hermès Paris. I always went without leather appointment and they still made it work.