I'm a big fan of testing keywords in AdWords before choosing the ones you want to use for SEO. You can set up the AdWords campaign today and get actual data on the number of impressions (number of times the keyword is searched), CTR and conversions generated by each keyword in only a few hours. I'm not sure how familiar you are with AdWords but it is absolutely critical that the campaigns be set up correctly from the get-go, otherwise you will get inaccurate data and may drain your budget quite quickly.
Since your goal is to test the keywords for SEO, make sure you are only using [Exact Match] keywords. And it is probably wise to uncheck the option to "Include plurals, misspellings, and other close variants."
Also, make sure you are not opted into the Display Network but rather just the Search Network (ideally just Google, not the search partners as well).
Finally, I'd suggest using a tool called LongTailPro to instantly come up with thousands of long tail keywords that you might not have considered yet. You can sort/filter by CPC, advertiser competition, organic competition, keyword competitiveness, search volume, etc. It gets the keyword data from Google and also uses the Moz API to check organic competition. It's definitely my favorite keyword research tool and one that I don't ever really see talked about on Moz.