You may upgrade or downgrade your package once a month.
Not necessarily, the features you need may cost less, and at the same time be more tailored to your website.
Overall traffic will be improved after approximately 90 days, after Stage 1 is completed (unless your website was penalized). Our initial goal is always to achieve the highest positions possible for your main search terms.
No, your traffic will likely grow from a variety of sources. Google, Yahoo, Bing, Facebook, Google+, Local ads etc.
Yes, it is likely to improve your quality score in Google Adwords and you will get more clicks for less.