This is Thailand, where the law and the application of the law arbitrarily meet. I’m sure that your girlfriend is a lovely person but a prenup could easily be discarded and you being rendered powerless.
it’s a PDF? Then google translate is your best friend. If not, simply download the English version from a US consulate and see what’s what. I would go in person. I’m sure the consulate will have English speaking staff. Good luck.
Any will do to get acquainted with the process as the rules are the same for everyone. But you will do the process through the one in Italy. BTW, it will probably take you a few weeks to work out the paperwork, so keep that in mind.
You don't need to fly from the US to come to Thailand. However, you will have to go through several annoying steps before arriving. I suggest that you take a look at the sandbox requirements at a Thai consular website. You won't have to quarantine if you're vaccinated.
Ipoh and Penang (you mean George Town) aren’t big cities... in fact, they’re smaller than Chiangmai, which is a rather small town. But you’re right: the focus is put on Bangkok. It’s the only real big city in Thailand, and by a massive long shot. To be fair, it’s a common practice in most countries: put the money on the economic engine of the nation.