Q1 - First, stop worrying about the big boys.
Quit worrying about siloing and SEO in general. You have the basics of SEO and following what you learned will work.
With WordPress your nav options are limited. Just set your sites up like the steps tell you to and you'll be fine.
With only 4 pages in 2 months you aren't doing much to encourage the search engines. How many links have you gotten to those 4 pages in 2 months? Seems to me you aren't doing the work you need to do and have the cart so far ahead of the horse that you are lost. Follow the steps exactly as they are.
How to play piano" (Main) and "Learn to play piano" are not the same keywords to the person looking for them. Use them both! Lol, on my acne site I have, "How to get rid of acne", "how to get rid of zits" and "how to get rid of pimples". Plus "How to get rid of pimples fast". All of those pages are unique as I wrote them. Yes they all cover the same topic. All get traffic and adsense clicks. If you don't put the phrases up because you think it doesn't look right you don't get the traffic. If you don't get the traffic you don't get the adsense clicks.
Q2 - You simpy need to get with it and get more pages up. 1 page every two weeks is simply not enough. It will be after you get your site established but it's not right now. Build your pages and stop worrying about all the other things. You don't have enough pages up yet for a good test.
Q3 - Personally I want the best content I can write or find. Google loves good content and so do the surfers. Surfers want a problem solved so solve it for them. I highly doubt you can ever have content thats "To Good". The better the content the more traffic you will get. The more traffic you get the more your ads will get clicked on. Your thought process is wrong. Follow the steps exactly and it will work.
Q4 - The IM niche is harder to sell in and get adsense clicks in. I have 3 or 4 sites related to marketing and they don't do as well as my hair or acne sites. Seems to me the surfers looking at them are more jaded than surfers looking to solve a personal problem.
Start getting 2 pages per week up until you hit 20.
Stop worrying about similar keywords and use them. They are search terms that bring traffic.
Do the SEO the way Mike teaches it.
Stop worrying about PR as that's all siloing is about. I have some PR 0 pages that beat PR 7 pages so you are worrying to much about little things.
Not in your list of problems but don't worry to much about DMOZ or Yahoo links either. I regularly beat them without using either.
Don't worry about .gov or edu links either. Doing research the other day I came across a site with over 300 .gov and .edu links and it was barely in the top 30. The majority of the sites above that site had few or not .gov or .edu links.
Go back, read the steps again and follow them exactly and they will work.
The things you are worried about aren't problems except for the fact you are letting them hold you back. Stop worrying about minor things and build your site out according tpo the steps.
If you want a sports metaphor you are trying to run the high hurdles and you have just learned to crawl. Build your sites, add pages, get lnks and you will start gettng adsense clicks.
My over all adsense CTR last month was 3.86%. Not the greatest but it was a new cash record and enough to pay the rent.