Rather a lot.
The best way to find it is to buy it and do a line by line comparison with the old one. However, if you don't feel up to that kind of effort, you could browse 40k forums, quite a few users posted their own summaries of the most important rule changes.
You'll find the answer in the Warhammer Rulebook or in the army book you are playing.
Musicians are normally use for moral purposes. You'll find the specific answer in the Warhammer Rulebook.
This rule can be found in the Warhammer 40K rulebook, but due to copyrights we are not allowed to answer this question.
This rule can be found in the Warhammer 40K rulebook, but due to copyrights we are not allowed to answer this question.
This rule can be found in the Warhammer 40K rulebook, but due to copyrights we are not allowed to answer this question.
This rule can be found in the Warhammer 40K rulebook, but due to copyrights we are not allowed to answer this question.
This rule can be found in the Warhammer 40K rulebook, but due to copyrights we are not allowed to answer this question.
To my knowledge Warhammer, Warhammer 40k, and The Lord Of The Rings are all completely different games produced by Gamesworkshop
This rule can be found in the Warhammer 40K rulebook (or Tyranid codex), but due to copyrights we are not allowed to answer this question.
Any Team can team up , unless it says not in the rulebook.
This rule can be found in the Warhammer 40K rulebook, but due to copyrights we are not allowed to answer this question.
Warhammer 40,000: Dark Vengeance would be a great start, as it has figurines for two armies (Chaos and Dark Angels) and a mini rulebook.