[eNotes editors can only answer one question per posting. If you have another question, please post it separately.]
As an English teacher, I can tell you that the Works Cited page does not only provide your teacher/instructor with the sources you have used to put your paper together, but it also helps him/her to gauge how much actual research you have done. As with any paper, you never want to rely more on one source than any other. If you are using parenthetical notation, it will be easy for the teacher to see if you have relied more one site or source than another.
As a rule of thumb, I have always expected a variety of sources from my students when writing research papers. It shows me that they have not only done their work, but that they have a well-rounded accumulation of knowledge about their topic. Using one site/source predominantly does not show that you truly understand the topic, the research process, or that you have an ability to construct a well-developed, well-organized or well-researched paper. And this is, after all, the intent of writing the paper: researching something factual (a topic in science, or a biography) or constructing a critical paper regarding a piece of literature you have read with supporting evidence, etc. For every academic level you reach, in high school or college, more will be expected of you in terms of writing a research paper.
(These are my own classroom suggestions having taught almost every grade level in high school, but everyone is different. The best way to know for sure is to ask your teacher. The fact that you are wondering if it's "bad" form to use too many quotations from one source shows that you are perceptive in the task of writing. Go one step further and ask the person who will be grading your paper.)
By the way, the best way to write a solid paper is first to follow directions; have a variety of sources; collect information if you think it can help and MAKE SURE to notate where it came from, even if you don't include it in the end. Using notecards can help because you can place specific facts on each of them in a logical sequence which you will then mimic when writing your paper. SAVE, SAVE, SAVE on the computer. Proofread repeatedly, taking breaks in between sessions to refresh your brain. AND DO NOT wait until the last minute to complete your paper. This is when a multitude of mistakes are likely to occur; also, the computer will crash or your printer will break or run out of ink.
Hope this helps.