Google keyword planner is not enough... Unless you are good in manual keyword research, i.e analyse top 10 competition yourself.
Google keyword planner won't give you any info on whether a keyword is rankable or not.
To analyse that, you will spend a lot of time to manually research. To save time, you would need a tool, okay, there are a few tools which a lot of people use. But still after using tool, you will need to do some manual checking to confirm it is really rankable.
i) Long tail pro
ii) Keyword revealer
iii) Keysearch.co - a newcomer
All of these tools are good, however, I am more bias towards long tail pro, while it is slower than the other 2 tools I mentioned, it has been around in the market for quite a long time, and is quite a standard that individual marketers use. ( And recently it change to use data from majestic seo which I found to have more data, compared to moz data). And the owner is quite a famous blogger/marketers which is more trustworthy.
* It is a bit buggy, and slower than the other 2 I mentioned, so just test and choose whichever you like =)
And yes , I am an affiliate of long tail pro. While it is completely optional, but if you consider trying it out, would appreciate you to click on my signature. I can pinpoint you on how to analyse for low competition keyword if you needed further help =)