Affiliate seo questions from a newbie

Hi there Warrior forum!

These last couple of months I started lurking around here and absorbing all the information I could, still, this whole forum at once can be a little daunting.
I had the idea of trying my hand on an amazon affiliate website and I started my first project a couple of weeks ago.

These are my questions and experiences, please give me some advice or guidelines if possible, I would be forever grateful.

So I started out by choosing a subject I know a lot about, skin health and especially people with skin diseases.
There is a lot of this going around but I did think I could provide high quality content to my viewers (as a lot of websites are just plain scams trying to take these peoples money in return for a "wonder" product => CLICK HERE NOW TO HEAL YOUR PSORIASIS ZOMG, INSTANT HEALED), you certainly know about the type of affiliate sites I'm talking about.

I purchased market samurai and started researching a shit ton of keywords that I could write a lot about myself. I came up with a big list of close to 5 or lower TACOMP (search engine competition) according to market samurai anything under 30 is pretty good so I guessed, even much lower can only mean better for me right ?

So I started the website on wordpress, it looks great, it has a lot of content, it has a couple of reviews with links to amazon, I don't rub it in their faces, it is really informative. Then I started writing posts based on these keywords, all high quality 700-800 keyword posts. I made 4 so far before I officially launch (it's still in maintenance mode, giving myself time to get things right)

I'm using YOAST seo and I always go for the absolute best results in yoast seo results. Long, quality posts with images, outbound links, nice custom pictures, etc etc

Now I've been reading up about XML sitemaps, tagging, canonical URLS and those are things I still need to setup, but I can manage that.

Here goes the advice questions:
-What about backlinks ? Is there good sources for quality backlinks ? Are they even needed with such low competition keywords ? I've been checking the backlinks for kitchenfaucetdivas (A very successful affiliate site) and they all looked like low quality to me... Then how does it end up on nr 3 on google search results when searching for faucet reviews ??

-What about anything else ? Is there a rule of thumb I should think about when building affiliate websites ?

-Any general tips are welcome.

-Things I should make sure not to forget before I launch it ?

-Is social media important for this kind of website ?

Thanks a lot !