Yes, the content is typically copyrighted in the year it was published.
Websites typically give the current year as the copyright year, as that's when the page rendered on the user's computer.
Typically no; there may be seemingly minor changes to the edition. However under current copyright law, duration of protection is based on the year the creator died, not the year the book was published.
Not necessarily; works are protected by copyright as soon as they are fixed in a tangible medium, but they may not be published for years or even decades.
Given current copyright law, it's merely a courtesy; the content of the site would be protected regardless.
In most cases, for work published after 1923, copyright will expire at the end of the calendar year 70 years after the death of the original author.
No. Under current US law, the fact that a website or its content does not have a copyright notice does not affect the copyright protection of that content. Copyright notice on published copies of a work used to be a condition of protection, but that requirement was eliminated decades ago, long before the advent of the Internet. Additionally, merely displaying content on a website is likely not an act of publication (unless the content is provided for download), so even under the old rules notice would probably not have been required.
Your own tweets, yes. Using others' content would require their permission.
You would want each issue to indicate the year it was published. Note that notification is not required for protection.
No copyright date is given in the book. It would be between 1888 (the year its prequel, The Hidden Hand was published) and 1899 (the year Southworth died). It is in the public domain.
The Adventures of Huckleberry Finn was first published in the United States in 1885, so the copyright date would be around that year.
A copyright lawyer specializes in the copyright portion of intellectual property. They may work for content users, content creators, or professional associations.
It depends upon where it was published, when, the nationality and residence of the author and what copyright formalities were in effect at the time. For example, a book published prior to 1923 in the USA has no US copyright. A book published in the USA by a US author in 1923 with copyright notice and renewal is copyrighted for 95 years. A book published in 1972 without copyright notice never had any copyright. A book written in 1899 but NOT published has copyright until 120 years after creation.