Should I upgrade to DW CS3?

Hello,
I Just finished a hobby site using DW MX2004 and Firework MX2004. I would like
now to make a more professional site, and wonder if I should upgarade to CS3
versions?
1) Is it possible that installing them will cause problems with the existing
files, htm pages?
2) Did anybody have any problem with backward comparability?
3) Would it involve a steep learning curve to use the new versions or are they
somewhat intuitive?
4) What are the best books available on Amazon.com to learn DW CS3 from?
Thank you for your help
Marianna