Under the studies of the Swedish polyglot and linguist E. Gunnemark,
the 80 most common words cover 50% of the everyday spoken vocabulary.
In other words, if we know the first 80 words in the frequency sequence, we can understand every second word in the conversation.

200 words will cover 60%,
300 - 65%
500 - 70%
800 - 80%
1000 - 85%.

Interestingly, starting from 500 there are mostly contextual words: bed, line, plan, fire.

We also see that after 500, each next hundred words covers only 2-3 percent of all vocabulary.

Thus, the number 500 looks quite logical and attractive to remain on it.

This does not mean that we plan to learn 500 words and stop there.
No, these 500 words are the necessary minimum that will give us the ability for basic communication.
The minimum that is needed for the minimum speaking skill.

In the future, we will use this skill and our vocabulary will grow naturally.