How suitable is opting for RethinkDB instead of traditional SQL for a JSON API?

I am building the back-end for my web app; it would act as an API for the front-end and it will be written in Python (Flask, to be precise).

After taking some decisions regarding design and implementation, I got to the database part. And I started thinking whether NoSQL data storage may be more appropriate for my project than traditional SQL databases. Following is a basic functionality description which should be handled by the database and then a list of pros and cons I could come up with regarding to which type of storage should I opt for. Finally some words about why I have considered RethinkDB over other NoSQL data storages.

Basic functionality of the API

The API consists of only a few models: Artist, Song, Suggestion, User and UserArtists.

I would like to be able to add a User with some associated data and link some Artists to it. I would like to add Songs to Artists on request, and also generate a Suggestion for a User, which will contain an Artist and a Song.

Maybe one of the most important parts is that Artists will be periodically linked to Users (and also Artists can be removed from the system -- hence from Users too -- if they don't satisfy some criteria). Songs will also be dynamically added to Artists. All this means is that Users don't have a fixed set of Artists and nor do Artists have a fixed set of Songs -- they will be continuously updating.

Pros

for NoSQL:

• Flexible schema, since not every Artist will have a FacebookID or Song a SoundcloudID;
• While a JSON API, I believe I would benefit from the fact that records are stored as JSON;
• I believe the number of Songs, but especially Suggestions will raise quite a bit, hence NoSQL will do a better job here;

for SQL:

• It's fixed schema may come in handy with relations between models;
• Flask has support for SQLAlchemy which is very helpful in defining models;

Cons

for NoSQL:

• Relations are harder to implement and updating models transaction-like involves a bit of code;
• Flask doesn't have any wrapper or module to ease things, hence I will need to implement some kind of wrapper to help me make the code more readable while doing database operations;
• I don't have any certainty on how should I store my records, especially UserArtists

for SQL:

• Operations are bulky, I have to define schemas, check whether columns have defaults, assign defaults, validate data, begin/commit transactions -- I believe it's too much of a hassle for something simple like an API;

Why RethinkDB?

I've considered RehinkDB for a possible implementation of NoSQL for my API because of the following:

• It looks simpler and more lightweight than other solutions;
• It has native Python support which is a big plus;
• It implements table joins and other things which could come in handy in my API, which has some relations between models;
• It is rather new, and I see a lot of implication and love from the community. There's also the will to continuously add new things that leverage database interaction.

All these being considered, I would be glad to hear any advice on whether NoSQL or SQL is more appropiate for my needs, as well as any other pro/con on the two, and of course, some corrections on things I haven't stated properly.