I started a thread on the Mac Studio launch (March 18th) that should be helpful in understanding how the U.S. Apple stores operate. There was a fair amount of interest in the thread, which runs 14 pages:
In U.S. Apple Stores, what's likely to be available for pickup on March 18?*
There are some posts above that talk about pre-ordering and the iOS Apple Store app.
Your ability to pre-order may depend on whether you're in the U.S. when ordering opens. I assume that you aren't in the U.S. now. Maybe try a dummy order to see whether you can actually access U.S. ordering and make an order for delivery to a U.S. address or store.
Similarly, it might be worth checking whether you can download the U.S. version of the iOS Apple Store app. I'll be surprised if you can install the app, and I'm sceptical that you'll be able to, even after arriving in the U.S., without changing your phone's region. Things may have changed, but I tried doing that some years ago, and was unable to without a region change.
I do think that you'll be able to order online once you're in the U.S. I can also tell you that you'll be able to use a non-US credit card for an online order. I'm in New York, but I use a non-US card myself.
* Further to the first post in that thread, I did purchase a base Mac Studio at an Apple store on launch day, but returned it and upgraded to the one in my signature. I expect supply of the iPhone 14 to be better than for the Mac Studio, which was initially very tight.