I have never worked with any version of EPiServer but will soon start working with EpiServer CMS 5.
My question is if I will benefit from reading "Developing Solutions with EPiServer" which is written for EPiServer 4 when I'm going to work with EPiServer CMS 5?
Welcome to the wonderful world of EPiServer! =)
"Developing Solutions with EPiServer" will of course differ in places if you are using CMS 5 as some methods/functions have been changed/removed/rewritten/added in the newer version, but much information is still the same.
That been said I would probable read the Developers Guid and Getting started in the SDK instead and go from there.
Hope you will enjoy EPiServer