K let me take you through a quick exercise. This may not be the right niche for you, but just use my example and find another. Just talking outloud and sharing the process I just went through real quick - DIDN’T do through analysis.
I would call the list you came up with "broad markets" - niches are smaller, more targeted and sometimes a SUB-niche of a market.
I went to SEOBook and typed in one of your broad markets - "Parenting". (Always start with the broad main keyword.)
Seo Book Keyword Suggestion Tool (I just start this this tool because it's in my browser, quick, no log in or captcha to deal with.)
I scan and want to go down quite a ways to get to some phrases that don't have a ton of searches because the ones that do typically also have lots of competition. Saw all different variations of parenting teens key phrases so that's a hot topic, but pretty competitive. Maybe one to tackle after you get more experience.
Kept looking and saw "parenting toddler" SeoBook said search volume was 21.
I liked that one because I have 2 toddler grandbabies. ALSO LIKE THAT ONE because you can promote books on parenting and also strollers, car seats and other baby gear. So there are products that go with the niche.
Then I go to Google and search: allintitle: "parenting toddler"
allintitle: "parenting toddler" - Google Search
Only 842 competing pages. That's really good.
allintitle: "parenting toddler
s" plural, which is probably how more people would search - 8,400 competing. Pretty competitive but not out of the ball park.
So then I go to the Adwords KW tool for more serious research and key in "parenting"
https://adwords.google.com/select/KeywordToolExternal
It gives me other suggested key phrases. Shows me the search volume (popularity).
There I see "parenting toddlers" 1900 searches in July
(It had 8,400 competing)
Then I see "toddler parenting" has more searches than that - 2900 in July.
So I check in Google and allintitle: "toddler parenting" only has 1,120 competing.
So toddler parenting has the best search/competition ratio and I would look closer at that niche.
So that's just a quick run down of how I do quick research. I just keep going back and forth between search volume #s and competing pages in Google til I find a phrase that seems like it may be good.
If I were an affiliate and was going to consider building a site around this niche I'd do a lot more research. I suspect in spite of what Google is telling me it may be competitive. There are also a ton of other key phrases to research like raising toddlers, how to raise a 2 year old and all types of variations. So that's just the tip of the iceberg.
I don't think there are any magic numbers in terms of how much search volume is enough and how much competition is too much. I just keep drilling down until I find something that has the best ratio.
I need to run. Am late for something and need to get going. So that hopefully helps give you a start.