The US is a common law country, which means law comes from a few sources: statutes (bills passed by Congress), administrative law (rules passed by federal agencies), and common law (rules derived from judgments in cases).
The US Congress passes bills (though at a somewhat decreasing rate in recent years). For example, in 2011, Congress passed ...
You are correct. From MPEP 211.05 A:
for a claim in a later filed nonprovisional application to be entitled to the benefit of the filing date of the provisional application, the written description and drawing(s) (if any) of the provisional application must adequately support and enable the subject matter of the claim in the later filed nonprovisional ...
Yes, that is permissible and defined in paragraph 6.18. For instance, US 7,756,129 is a grant with 401 claims, although they are not all in serial as in your example. Keep in mind that writing dependent claims in serial creates easy targets for invalidating large numbers of your claims.
¶ 6.18 Series of Singular Dependent Claims
A series of singular ...
Yes, claim amendment is allowed during an Office Action as long as the amended claim language fits within the original disclosure and background.
The information you are looking for is in MPEP Chapter 0700 (Section 714) 37 C.F.R. 1.121 Manner of making amendments in application, under item (c) Claims.
I don't know where to start?
For starter you should read the USPTO patent applicant checklist on filing patent and its basic requirements and gather information listed therein. LINK
what if inventor or applicant is not from the USA?
Most of the countries prohibit direct filing of patent application to foreign countries. These are called security ...