Wondering if it’s worth targetting 3 worded key phrases that have 100,000-500,000 results in quotes? Keep in mind the 1st page is full of crappy shopping results like amazon, squiddo, shopping.com and many unknown webpages that don’t specifically target the keyphrase and don’t have it in their domain name? Is it likely I’ll get on the 1st page in this scenario?
The estimated number of pages in results is not a reliable indicator of competition. It only indicates the general size of the competition, not the strength of the competition. You could have a relatively small number of pages, yet have a couple dozen really strong competitors that will make it very difficult to reach the first page of results. Alternatively, you could have a large number of estimated pages, yet have few strong competitors and rank well quite easily.
To determine how hard, or easy, it will be to rank on the 1st page of SERP, take a good look at the web page listed in position #10. That’s the only web page you must beat to reach the first page of SERPs.