The other thought I had was a revelation that was revealed quite a few games into learning how the Sisters played in 40K.
They arent a shooty army. It seems like such a simple thing to say, but when I finally grasped that, my playstyle altered and I did a little bit better.
Fielding an all-Sisters force, I had exactly 3 shooty units, and sometimes 4: 2 units of Retributors, each with 4 Heavy Bolters, and 1 or 2 Exorcists.
The rest of the force was Battle Sisters, which combined with the Book of St. Lucius and Faith Points for Invulnerable 3+ saves, meant I could get them stuck in and they would hold. They might not win, because in HtH the Sisters just werent awesome, but they would hold up important units while my other short-ranged units jumped around:
Counter charges from arco-flagellants
Hit-and-Run on my Seraphim (2 units! Loved 'em!)
Drive bys with Dominions
As of right now, looking at the list, that is how a list would shape up. The Exorcist is an AWESOME tank, and Im not sure 2x AT4+ is good enough for it, because 45cm range is horrible

The only other ranged unit in the army is the Retributors, or IG backup.
Because of this, the CC of the army needs to be spot on. I dont think you can skimp here, because like the Tyranids, the Sisters need to get stuck in to do their damage. They have no long ranged firepower without IG Leman Russes added to IG Infantry, a Titan, or Baneblade. Their army should play like this.
Thats all for now!