For question 1 I would not use absolute positioning, but then I never use absolute positioning, instead I would use margin-top: 200px on .top, it should get the same effect depending on the rest of the layout.
I know this doesn't exactly answer your question, but with an unknown amount of text being present within .top it's the method I would/do use.
For question 2
http://alistapart.com/articles/fauxcolumns/ explains it quite well, in truth unless you fix the height, the 2 columns really won't be the same height but they will look it and that is all that matters.