How many words can I learn each week?
How many words you can learn depends on what you mean by learning (see: What does it mean to learn a word?) and how much time and effort you are prepared to put in. It also depends on which words you are learning.
As a beginner or low level student, you will need to learn many basic words, which you will practise often, as they are very common in the language. This makes learning words quicker and easier, and you can learn a lot of new vocabulary.
However, as you advance, you will be learning less common words, and you may also be learning more difficult, abstract words. These words are ones that you need to understand in your studies but which are not so frequent in everyday life. This will slow down your rate of learning.
As a rule of thumb, experts in learning (Miller, 1956) tell us that we can learn seven (plus or minus two) items of information at a time. This suggests that around seven words is probably our limit at any one time if we really want to remember them. There is no point in studying lots of words just to forget them a short time afterwards! For most people seven words a day is probably the limit, although some people might increase that by having two study sessions a day. You can learn better and make the words you learn more memorable by using effective study techniques. See: What is the best way to learn new words?