What I usually do is write down my interests with about 5 keywords for each interest; then I choose one interest from my list and take one of those keywords I thought up for that interest and go to my favorite FREEBIE tool, seobook. Here's how:
(1) go to www.seobook.com (2) click on the grey, JOIN FREE button all the way at the top right corner of the page (3) fill in your email address and pick a username (I just used my name) and checkmark the little box to get some free goodies (4) a page will pop up that says "thank you for joining". THEN, all you do is (5) click on the blue "TOOLS" button, and a drop down menu will appear (6) under the "Public" list, choose "keyword tool". THEN (7) click the blue SEO button on the top bar, and again, choose "keyword tool". LAST BUT NOT LEAST you arrive at the Keyword Tool Page.
Put in your keyword or keyword phrase, making sure the 2 little boxes called "G Trends" and "More" are checked. CLICK blue "Submit" button and be prepared to be very happy with the results!
You'll find that it gives you a list of related terms people have searched for in your niche, how many monthly searches there are, and so much more!

Yes. Search the competition the affiliate programs available for each niche and then decide. I wish you the best of luck.

I know -- I had that same issue and still my niche (scrapbooking) is too broad. We're just too talented. lol

Sounds like a good idea, Research61. Keep up the good work!