as far as your priest goes, try something like this for the primary castsequence
/castsequence reset=9 Vampiric Touch, Mind Blast, Mind Flay, Mind Flay

This looks good
Code:
  #show Mind Flay 
 /stopmacro [channeling]  
/cast [nostance] shadowform
In this set the “exists” conditional is not required as both “harm” and “nodead” infer “exists”

Code:
  /target target=target, harm, exists, nodead][target=party4target, harm,  exists, nodead]
[target=party1target, harm, exists,  nodead][target=party2target, harm, exists, nodead]
For this I really believe you would be better off breaking it into a couple macros.
The First of course is that now that vampiric embrace is only affected by Mind Blast, a sequence could be created specifically for that.

Code:
  /castsequence reset=target/combat   Vampiric Embrace, Shadow Word: Pain, Vampiric  Touch, 
Mind Flay, Mind Flay, Mind Flay, Mind Flay, Vampiric Touch, Mind  Flay, Mind Flay, Mind Flay, Mind Flay, 
Vampiric Touch, Mind Flay, Mind  Flay, Mind Flay, Mind Flay, Fade, Vampiric Touch, Mind Flay, Mind Flay,  
Mind Flay, Mind Flay, Vampiric Touch, Mind Flay, Mind Flay, Mind Flay,  Mind Flay, Vampiric Touch, 
Mind Flay, Mind Flay, Mind Flay, Mind Flay
This piece of code will never be reached as only one command with a global cool down can be done per macro. If how ever you moved this to the front and added a conditional, I believe it would work well for you.
Code:
  /castrandom Devouring Plague, Mind Blast, Shadow Word: Death
So, overall I would suggest a change to something like this.

Code:
  #show Mind Flay  
/stopmacro [channeling]  
/cast [nostance] shadowform  
/target [target=target, harm, nodead][target=party4target, harm,  nodead][target=party1target, harm, nodead]
[target=party2target, harm, nodead]  
/castrandom [mod] Devouring Plague, Shadow Word: Death  
/castsequence reset=target/combat Vampiric Touch, Mind Blast, Mind Flay, Mind Flay, Mind Blast, Mind Flay, Mind Flay
This will cast either Devouring Plague or Shadow Word: Death if any mod is pressed, if no mod is pressed it will move on to the cast sequence. This sequence is timed perfect as long as you have at least four point in Improved Mind Blast. A total of 9 second sequence.

As far as moving fade out, with the addition of removing all movement impairing effects I would think this would be much better being off the macro so you can cast it at more opportune times.