Unless he has an H or an L visa, if he leaves the U.S. and then returns and files for AOS his immigrant/non-immigrant intent will raise red flags...

What will happen if the tourist marries to US citizen

It is certainly possible, although there may be some possible immigrant issues that can cause you problems when applying for permanent residency...

More info. is needed to accurately answer the question. Consult with an experienced immigration attorney.

US citizenship (n400 application)

The time can vary by office, but on average you should receive a notice within 2-6 weeks based on where your application is at in the process.

What is the process of me marrying a U.K. Citizen here in America?

Ms. Agarwal is 100% correct and described your options perfectly. The requirements can get cumbersome quickly. Consult an experienced immigration...

Permanent residency restrictions

You can stay outside the U.S. for up to 180 days on any one trip. If you stay outside the U.S. for longer than that (but less than one year) there...

How to start a "follow to join" immigration process?

I second the response from that of counsel before me. You will need an experienced immigration attorney to navigate the case through the...

No, kids are not necessary to get an I-751 approved (although they would certainly help). Proof over the course of the two preceding years of the...

Can the USCIS ever not make a decision on someone's case?

You can file a lawsuit in federal court to force them into making a decision. Talk to your lawyer about this option.

immigration Court is its own animal and quite different than "regular court". That said, every case is different and some of course are better...