the answer is of course yes, but when you practice and use the language often it doesnt become a matter of memorization. The words start to come naturally and you dont have to give a lot of effort to remember the word

That depends on what you think of as "a lot." About 1,000 words is a good amount for daily conversation, but to be very good you'll need about 3,000 words. Focus on the most frequently used words and you will be able to say more, faster.

In the end you will remember many words. Also as a result of using the language. If you have to speak English everyday you will remember words automatically. If there is no real need to speak English it will take more effort and the amount you have to learn conciously will increase. At least that is how I experience it.

Quite necessary yet not sufficient.

Definately yes, I think. =)