Thing is, the answers are nowhere near straightforward.
Your first question, about taxes, is particularly complicated. Here are the relevant tax treaties:
https://www.irs.gov/businesses/international-businesses/unit...
While they seek to prevent double taxation (and tax evasion), they are packed with dense legalese full of clauses and subclauses designed to make certain types of income taxable in different places. To navigate that question, you'd need a highly experienced tax accountant/attorney with specific experience in UK/US tax treaties. Moreover, that person would need a strong understanding of what you do, how/where you sell, and how/if/when you plan to pay yourself.
Your second question is even more complicated. First, if you incorporate in a country like the US, your corporation is considered a person in that country and is thus bound by that country's laws. I trust that you did enough research to know that.
Second, recent history has demonstrated that the UK (as a Five Eyes nation) shares intelligence data with the United States. Moreover, recent history has demonstrated that the UK will work at the behest of the US intelligence community. This is governed by years of treaties and high level agreements. Consequently, the first thing you need to wonder is whether your government would just hand everything over, regardless of whether you have a US corporation or not.
Third, if you do incorporate in the US, you would be subject to US law, but US law can generally be fought in a court. The question becomes whether or not you could afford to fight an NSL. Could your business afford a long, highly distracting process where it is you versus a government??
But then, you need to look at yourself. Do you have any secrets that could be used as leverage against you?? If you plan to fight a well funded intelligence agency, you'd need to be prepared for them to fight hard.
I tend to argue that if a well funded intelligence agency truly wants information, they'll get it.
So, while your questions were honest, they were anything but straightforward. And, they aren't actually relevant to Atlas.
Rather, you and a group of experts need to sit down and figure out the costs, potential costs and the benefits of incorporating in the US. If it still makes sense, Atlas is a tool. But Atlas can't help you navigate the complicated relationship between your company, international law, agreements like NATO/other intelligence sharing agreements, EU law and two (possibly three) tax authorities.
And, with all due respect, neither can Hacker News. Every situation is so different that anyone who is qualified to answer those questions wouldn't as they understand how deeply complicated they are.