I have an ecommerce website which is running google ads, so I have the list of converting keywords. My strategy is:
0. Start a blog, domain name start with my main keyword, content focused on the niche of my ecommerce website.
1. Go to upwork, post a job with one of my converting keywords, hire someone to write blog article, focused on that keyword.
2. Post this article to my newly created blog.
3. repeat this process, have all my converting keywords written.
4. when there are traffic to my blog, put a button on it and point the link to my ecommerce website.
My questions are:
1. Is it a solid strategy? any flaws?
2. How can I control the quality of the article? I'm not a native english speaker, have little to no experience on copy writing.
3. Any software/tools to give the article a score? I know surferseo has an editor, there is a score. Any alternatives?
Thanks
Check on ahrefs.com the volume of monthly searches per kw + the difficulty to rank on each one. That will give you an idea if the amount of extra traffic you can generate is worth the time and investment.
If you already have convertirlng keywords, you could also optimize the conversion rate of your site, or add upsells to improve the profit per customer. That would result in faster improvement than an SEO strategy.
As jeremie suggested, it's always good to check the KWs with some research tool to see what the competition is like and what the search volume is.
I do have an active AHREFS subscription, so if you'd like to check some KWs I can do that for you 
Now back to your plan :
Starting a blog and then trying to direct the traffic to your ecom website is an option, but why don't you start the blog directly on the same domain?
SEO is not just about content, there are many other factors... if you start a new blog, you will start again from scratch, if you put it on the domain where your ecom website is, it will benefit from it's strength that it has already built. It will also improve the internal linking structure since you could link to the blog from other parts of your store.
You will also need to think about how to get backlinks to the blog pages as they won't really rank without them.
This is what I would do:
- Start the blog on the same domain
- Identify KWs that have potential and come up with topics that you can write about in way that would also allow you to sell your own products.
EXAMPLE: Let's say you have some products that are good fit as a gift.
I've run a quick search in AHREFS for kws that contain "best gifts for", I selected KWs with at least 1000 monthly searches and I ordered them by the ranking difficulty starting with the ones with lowest competition.
You can see the result on the screenshot below:

As you can see, there are several keywords mentioning the age of the person the gift would be for and some of them are low competition KWs. Based on this, I would write a blog post about "best gifts by age" and list the options in age categories . And obviously, anytime one of my products would be a good match, I would list those.
The next thing to do is to find ways of obtaining links, every blog post needs some in order to rank. Internal links will help too, but external ones help more. You can buy blog insertion links or guest posts on Fiverr, but MAKE SURE you properly research the website you are buying from first. You can use public places that allow posting articles with links included... Quora, Medium... There are many ways but that's a topic for another article.
Find another KW, select topic and repeat 
There are two reasons why I start a new blog instead of post on my ecommerce website.
1. my ecommerce website is on
2. I think it will mitigate the risk of put everything in one basket.
But after I read your replies, I think it's a good idea to put everything together.
The Progress:
I ordered my first post on upword, very solid. costs $100 and 3,000 words length. The next thing is link building. I will repeat this process and see if it works. SEO is a long term strategy, might need different mindset than media buying.