Can I start with Electron as a (still) relatively new to JS?
Electron does nothing more than stick together a NodeJS instance and a Chromium shell. Basically, you have to write a front-end and a backend (just like for a website), but they will be one app later on. If you want to write a small app with that, I'd advise you to first get some NodeJS knowledge, so you feel comfortable and then just dive right into Electron. It's not difficult :)
Does it make sense to learn React in order to do small apps
NO. Please don't. Stick to vanilla JS until you feel very comfortable with it. All those crazy frameworks all solve particular problems*, but as long as you do not have these problems, using frameworks will just make stuff more complicated for you and limit your ability to work with different frameworks or come up with an original solution on your own. Learning vanilla JS will enable you to pick up any framework you like within a matter of hours later on, in case you really need it.
\* For example React was created by Facebook to solve their problem of having many separate widgets on their site and needing to somehow develop and (re-)use them separately. Nothing you would ever need in a small application (and nothing you ever need if you know about proper strict CSS based decoupling, however that's something for another discussion)
Maybe with my goals I should switch to Python
To be honest, I think that Python might help you with some of your goals, like data manipulation and especially with analysis. There is a load of libs out there for lots of different use-cases and scientific purposes. Python also allows you to see results at once (at least when using the terminal...) and you can develop small applications using Python plus a GUI library. Qt would even be pretty easy to pick up, because their GUI ML (called "QML") is pretty similar to HTML/CSS in many places, which you already know.
However, when talking about switching between languages, I usually think that there are many different languages out there, so you really should at some point start picking up a second language, so you can develop a greater variety of applications. For my hobby projects and work, I had to pick up quite a number of different languages (like C, C++, Delphi, Object-Pascal, Basic, Rust, Python, Java, C#, PowerShell, Bash, CMD, STL, JavaScript, PHP, TypeScript, CoffeeScript, Perl, etc.), and I think that once you understand the basics of programming and logic, it's just learning a different way of doing things, syntax, standard library and a few small quirks.
To put it into a nutshell, I think that you should do what you want to do and what keeps you motivated. Check how others solve certain problems and try to imitate them. If that means picking up another language - why not? You can only gain experiences by doing so (as long as you don't start leaning 10 languages in a month, which surely isn't healthy). Also check out the FAQ for new developers, you might find a few more answers to possible questions in there :)