My problem is: exactly what I know is not sufficient ;-) I know JS. The backend layer for me is unchartered territory, DBs I've shunned most of my career. So some learning curve can't be evaded.
And from looking at the view-layer competitors to angular (vue and react) I'm not sure why not to give those frameworks a try, as Ionic seems to be less 'native' and more 'webView' oriented.
Database Design for Mere Mortals: https://www.amazon.com/Database-Design-Mere-Mortals-Hands/dp...
This is the book I recommend to everyone who is shy about DB's - I have owned several copies and given every one away. It breaks down not only functionality but how to create a good design in a sensible and easy to understand way. Worth every penny (and now somewhat cheap)
It seems to me that Jim Melton's Understanding the New SQL was pretty good. Anyway, I'm pretty sure I read one of Melton's books when I was learning about databases.
I always thought of the NoSQL movement as encompassing document, KV, and GraphDb's and each can be a major departure from RDBMs thinking. These technologies aren't always "replacements" for RDMB's and often live alongside them, Redis (or memcache) and Solr/Lucene (or elasticsearch) are ones that I have personally used the most.
As you move into other tools like Cassandra or a Graph DB they look shiny but you are making some major (and maybe worthwhile) trade offs. These sorts of decisions probably shouldn't be made based off of knowledge from a book but rather experience and more importantly testing (performance and use).
As a side note, the last project I did ended up using a flat file as a back end because it was fast, simple and easy while meeting the needs for what it had to accomplish. Installing a DB was more work than needed.
Assuming you're doing a small application with standard features, you should be able to pick up the basics over a weekend. It is a different story if you have to scale to tons of users, improve performance etc, but for a normal application, designing a bunch of tables shouldn't be hard.
The backend layer for me is unchartered territory
This might take a bit more work than the DB. My you know JS, so maybe you could pick nodeJS for the backend?
Unless of course the real "side-project" is learning a new stack[0], you want to set yourself up for success by using what you're already familiar with.
[0] This can be completely valid and worthwhile—just be honest with yourself about whether your goal is to learn something new or to solve a problem or to create a business.