Are there any open source data that categorizes English words based on CEFR levl and is available to download? As an example I found https://www.oxfordlearnersdictionaries.com/wordlists/oxford3000-5000 , which categorizes English words based on CEFR level, but it has license.
This link appears to have a few lists of words based on level. It's not sortable like the EVR, but the content is still there.
I'd recommend putting the words into something like Anki. Anki has open source flashcard sets, so anyone can use the flashcards that other people upload to it, and they allow you to flip through flashcards giving each a rate of confidence that will determine how often the word shows up again. It looks like they don't have a dataset for English CEFR vocabulary by level, but I have seen some lower level CEFR vocab sets on quizlet
It also looks like although the vocabulary lists are licensed, you can use a text analysis tool from the same website for free to test your writing skills after you've gotten more of the vocabulary down.