Update #1
I've picked up 20 keywords for the first content batch. As you'll see below, they are very different in metrics and SEO difficulty. The reason lies in my desire to learn as much as possible from the very beginning.
I said earlier that I'll take Semrush or Ahrefs free trial when the site will have some content, but I've changed my mind and paid $0 for a Semrush 7-day trial. Now I need to find at least 100-150 keywords, and then later I'll do the same with Ahrefs.
For now, Semrush seems promising.
Let the experiments begin.
Keyword #1

This is the article I've already published and it ranks pretty well. In fact, it sits on position #1 for a few months. The content is ca. 3k words long but it is unreadable and full of copied and translated paragraphs.
The conclusion: long-form shit ranks well.
I'm only concerned that it will lose the number 1 position with time, so, although I don't have any proof for this statement, I'll pick a writer from Fiverr to rewrite it and some visuals.
I've already hired one Fiverr (India-based) writer and paid $25 to do this, but the result was worse than it is now. So I've canceled the order. I have some experience with Fiverr (30+ articles for another project) and I found that India or Pakistan-based writers never perform well in my niche. On the other hand, I was more than satisfied with the UK and Eastern Europe-based writers.
I've also tried the content agencies and expensive, native US writers, but it wasn't worth the money. The content agencies were the worst - they hire writers who know nothing about the subject.
Now onto the next...
Keyword #2

This one seems like a piece of cake, but after manual SERP inspection, I found that the site (the direct competitor) which ranks #1 for this KW has 6.9M monthly search traffic and thousands of backlinks. The good thing is that there are no videos or snippets and all other SERP positions are weak. I think I could rank in the top 5 here.
Keyword #3

Here we also have the 6.9M site at SERP #1 and #2. The good thing is that #3 and below aren't relevant to the search term at all. For example, the #3 site is an online shop, #4 has only 300 monthly search traffic and a 300 words unrelated article. The aim is to rank in the top 5 here and maybe pick up some other keywords by the way.
Keyword #4

This one is difficult, but I'm an expert in this domain and have a ton of experience. I'll write this article myself and ad some super high-quality illustrations. So let's see does Mr. Google respects high-quality content. Long-form, of course (at least 3k words).
I personally don't believe so, but on the other hand, it may pick up some good backlinks. I've seen that a lot of my competitors have Wikipedia backlinks, so I need to dig deeper and find out how they got them.
Keyword #5

This one should be easy. I'll hire a Fiverr writer for this article. There are no relevant SERP results, so I'll go for the #1 SERP position here.
Keyword #6

Although the Semrush says easy, here we have the 6.9M site again at #1. The manual SERP inspection revealed strong and relevant domains ranking up to #7. None of those content is transactional. I'll be more than happy with the Top 10 SERP position.
Let's see how much we can trust Semrush KD score.
Keyword #7

This one should really be a piece of cake and I am certain I can rank #1 here. The interesting part with this keyword is the YouTube video above the #1 SERP position. Here we'll see how much of the traffic can a video take. This keyword is very similar to Keyword #1 that I already rank #1 but w/o video above #1 position.
Keyword #8

This keyword is difficult by any means. I would give it KD of at least 80%. SERP is full of strong sites with very relevant and quality content. The reason I'll go with it anyway is that I want to build an authority site and this is something that is very important for the reader. I also have a lot of experience and knowledge here so I'll write this article myself.
If it is about the traffic, I would never choose this KW, but as this is an experiment, it is a nice addition to "low competition" keywords.
Keyword #9

This one is a golden nugget:
Position #1 is the site with 1.5k monthly search traffic and 3 backlinks, #2 site has 500 monthly visitors and it all goes downhill from there... Plus no videos, and just one snippet. I'm quite confident I can rank #1 here with a $20 Fiverr article.
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So that's it for the "experiment" keywords. As I said, I have 11 more KWs that I know I can rank for to get some initial traffic. When I publish the articles, these 9 examples will serve us to learn more and adjust the strategy accordingly.
The next step is to research the topics and prepare the briefs for writers.
Stay tuned.