Right ive got a problem i want to build/convert a new army based on the EOT L&D army rules! however i want to add allies to my current L&D army.

Mainly to save myself money! plus there not yet painted in any particular
colour/fashion which helps!

So what i need to know is can i add Emperors childeren CSM's to my current traitor guard army as allies??
could this be done if i for example had my arch heretic with the mark of slannesh??

also the other question is......
In the EOT codex it says you can pick the following allies from codex CSM's
1 HQ , 1 ELITE , 2 TROOPS , 1 FAST ATTACK choice!

Could the HQ choice be a lieutenant or chaos sorcerer?? that way i would have 1
HQ unit for my L&D & one for my EC CSM's hence 2 HQ choices!

For the troops i could have EC CSM's ! that way i'd have both a HQ choice & 2 Troops choices!!

please reply as its something i'm slightly unsure of!