To answer your final question, yes but not really. You can definitely use AdWord keyword planner tool to get solid organic search volume estimates. However, don’t just stop there. Leverage other tools to find longer tail variations you can map against various stages of the buyer journey. I like to use SEMrush, Keyword Tool.io and Google autosuggest.
Be sure to re-evaluate these keywords every few months -- once a quarter is a good benchmark, but some businesses like to do it even more often than that. As you gain even more authority in the SERPs, you'll find that you can add more and more keywords to your lists to tackle as you work on maintaining your current presence, and then growing in new areas on top of that.
We at Moz custom-built the Keyword Explorer tool from the ground up to help streamline and improve how you discover and prioritize keywords. Keyword Explorer provides accurate monthly search volume data, an idea of how difficult it will be to rank for your keyword, estimated click-through rate, and a score representing your potential to rank. It also suggests related keywords for you to research. Because it cuts out a great deal of manual work and is free to try, we recommend starting there.
In a nutshell, Long Tail Pro helps you quickly find keywords in bulk based on a seed keyword that you input. In addition to returning hundreds of related keywords, the tool also shows search volume (monthly search volume), advertiser bid, number of words, rank value, and my favorite Keyword Competitiveness (helps you judge the competition and keyword difficulty).