Long Tail Platinum - Choosing keywords for my landing page

I have an interactive information product which I have nearly finished creating. This is the first information product I've ever made and I neglected to do keyword analysis first as I should have done. I am at the keyword analysis phase now.

I plan to charge approximately $40 for this information product. It will also be a page under a domain which I will also use to post at least 30+ articles (most likely many more since I'm passionate about the subject and there are many keywords available for this topic).

I just used Long Tail Platinum to narrow down the list of keywords I just found to 5. Here is a brief overview of my list:

Keyword 1
Average Keyword Competitiveness(KC) = 38
Local monthly searches = 1,600

Keyword 2
Average Keyword Competitiveness(KC) = 38
Local monthly searches = 2,900

Keyword 3
Average Keyword Competitiveness(KC) = 38
Local monthly searches = 1,300

Keyword 4
Average Keyword Competitiveness(KC) = 27
Local monthly searches = 390

Keyword 5
Average Keyword Competitiveness(KC) = 29
Local monthly searches = 260


Regarding the top 10 Google results for the first 3 keywords, I noticed that the domain authorities are mostly over 60 and the page authorities are mostly over 40. For each keyword, more than half the results have juice inks under 10. All CPCs are good.

Should I take the risk and choose one of the first 3 keywords with higher monthly local searches since I'm going to build the overall traffic of this website over time? Would choosing any of the keywords with under 400 monthly searches be a huge issue since this is for a landing page with a $40 information product?

If it makes a difference, I will also write an E-book version of this information product which will contain links back to the main domain address and the landing page address.