This may be the single best Battle sister picture there is, for the simple reason that you alone have depicted them wearing power armour, rather than PVC catsuits.
Power Armour is bulky and inflexible - but no other artist seems to remember that. You have depicted it perfectly.
The only criticism that comes to mind is that two of the sisters (Centre and far left) seem to be missing their backpacks.
No, you are talking about the Chaplet Ecclesiasticus which is an ][ with the sun symbol halfway down with or without a skull in the centre.
Or an ][ with wings.
Or an ][ with two, not three strikes through the centre.
And in a few odd cases just and unadorned ][.
The Chaplet Ecclesiasticus is the symbol of the Ecclesiarchy and the Sisters are first and fore-most the standing army of the Ecclesiarchy.
The Inquisition Rosette is the ][ with three strikes through the centre. It may have a few other iconographies on it as well but the three strikes is the important part.
This is correct.
The Sisters of Battle have a ton of ][ symbols on their gear - the ][ stands for 'Impirator' - Latin/High Gothic for 'Emperor'. The Emperor's signature was a simple letter 'I'.
The Inquisition =][= has two or three strikes through the center (It varies depending on artist).