That is going to depend on the situation. If it is part of a sentence, you should, however, it may not then be rendered in the document as a hyperlink. You will have to figure what works for you.
No it's not necessary.
No, it is not necessary to put a full stop after "Dr." unless it is followed by a sentence.
Address Bar...
no
You can't play Saints Row 3 on a website, it's a full game of several gigabytes, played on PC or console.
no
If the full stop is at the end of the initials then there should be a space before the next word.
I don't know exactly what you're saying, but a way to get to a website without typing in the address is to put in the ip address. Every website has four numbers separated by periods that brings you to the site. For example, if you put 74.125.224.240 in your address bar, it will take you to google.com
Google.
yes
If it is at the end of a sentence then yes however if not then no
full stop, it is only reasonable because whenever you end a sentence you put a full stop roughly 97% of the time