I started coding later in my career. I had been doing HTML and CSS from when I was about 25, but that was just a bit on the side while I was a product manager. I got into server-side languages and then lots of javascript front-end when I was 32. I've learned tons, enjoy coding, but I am also now transitioning into a CEO role after having transitioned back to Product Management just over a year ago.
You mention 'more complicated languages', which I think is the wrong perspective. The language itself shouldn't be considered complicated, it is the overall structure of your application which contains complexity. Data structures and architecture choices will dictate the challenges you'll experience more than the languages. Languages are, for the most part, about semantics.
I think you're a bit ahead of the game in having selected a project to work on. This is how I started coding, and having a vision you are working toward, I think, is a very good thing. A few friends who have wanted to take up coding over the years, never got very far because they would try a few tutorials, but never had their own project to try to adapt what they were learning to.
It will be very difficult for you to check code quality without knowing how to code. Even knowing how to code, you have to be pretty good to look at somebody else's code and judge it to be of quality or not. This is something I've often struggled with, until you're in there mucking around with it yourself and then you will have a better idea of what might be good or bad. This is assuming there are no massively stand-out 'this is horrible' type issues, but more recognising things that may become issues in the future.
So, with startupblink, did you pay somebody to build this? Or have you built it yourself? (I'm hoping it's the latter). If you've built it yourself so far, I'd say you're off to a good start. If you've paid somebody to build it, I think there are some issues (unless you didn't pay them much).
As far as what languages to learn. Front-end will always need javascript, but now you can also run javascript on the back-end, which means you can learn one language and use it in both places.
You can run javascript in a lambda (or google function) which means you don't have to run your own server, and it will likely be free for you. You can also learn how to use dynamodb for your database, which will probably be easier than learning sql at first as you'll be dealing with documents rather than tables and indexes and stuff.
One important thing to keep in mind is that you are going to make mistakes. You will spend a week building something, and then throw it away. That's going to be part of learning. You're going to come up with a feature, write it out, build a structure around it, and then you're going to learn something new and you'll get rid of what you wrote. To many people this will seem like a waste of time. It isn't. It's learning. We all do it to some extent, but I think you get better as you go.
I don't know about schools and courses. You didn't say where in the world you are, or if you know other coders. I was self-taught before online courses existed. You could try a code-academy, or figure out if you have connections to a good developer who may be able to help guide you.
Be prepared to bang your head against a wall, but learn to make it feel like you're not banging your head against a wall.
It's a challenging road to take, but I feel a worthwhile one. Though I will be coding less and less in the future, my understanding of coding will continue to serve me in the future. I suspect you will find the same.
Best of luck.