Spend at any of the airport stores worldwide (I guess you mean Changi here) will not be reflected in SG profiles or any country purchase history. (They might be able to see Duty Free purchases in some stores in other countries, but it would not really count either. I can think of Qatar possibly France, as examples.)
Purchase history in SG tends to be significant only in that one store.
I know that there is access to worldwide purchase history if they so wish, at a higher level and definitely at FSH, concerning mostly QBs.
I would personally advise starting your relationship the store where you find the SA with the best fit for you. With Hermes, a good SA is really quite crucial.
I agree and do not think telling a new SA right away you want bags is the way to go, but it can vary for different people.
With the current situation, trying to start multiple profiles in different countries is going to be tough simply because the time + effort is so much more than before. I think Hermes Corporate in general is encouraging clients to shop at their nearest home store and concentrate on that one account.
I do have to say that I didn't follow much of this but that was because I was very blur when I started shopping H years ago. Much has changed since then as has been shared by those who have much longer experience with Hermes than I do.
Good luck!