I'll talk more about this in a video soon, but you can group pages around similar or related phrases through cross-linking. This way, as each page builds authority on it's specific phrase, all of the pages gain authority on the more general phrase.
Definitely. Always write for humans first, but you should definitely use the phrases you are targeting in the page (especially in the first and last sentence, title tag, header tags, and links to and from the page).
The first page to gets indexed gets the credit. You can publish articles to article sites first if you want the backlink, or your site first if you want to optimize for that page.
I look for phrases generating hundreds (200-800) searches a month, at least initially. Above that and there's likely to be lots of competition. Below that and it's not worth the effort. If you can rank on the first phrase for 10 phrases like this, you'll get some decent traffic to your site. Also, more specific phrases tend to be more relevant to your market and are a sign that the searcher is seriously looking as opposed to casually browsing.
You want the least competition possible. There's always going to be competition, and in some markets/lines there's more than others, so I really can't give a hard and fast number. It's definitely not getting any easier, though as the search engines prioritize local sites more, there are more opportunities to rank in a specific region.
