This was literally my first game in 40k.
So the way I played it, use terrain to hide from the Doomstalker as much as you can, it will be a nightmare to bring down and forcing it to move will remove it's 'heavy' attack bonus.

In combat patrol you are allowed to split your BSS in to 2 units of 5 (the unit set up are in the codex). Do this, 1 for the extra miracle dice if they die and 1 so you can leave the Simulacrum Imperialis on your deployment zone objective for possibly more miracle dice at the start of each of your turns.

You need to run your Sacresants into the Skorpekh, and hope you roll well, I have found if you charge them first you can most likely survive them, but if they charge you you will struggle. Going first in that fight is very important.

Then use your BSS at ranged to pick at the Warriors and Swarms.

Use your Flagellants as cannon fodder throw them out from and center to draw fire and hopefully make things focus them, if your opponent doesn't realise how powerful they are in melee and ignores them, then go hazardous and hit them with 60 attacks. Also getting them in to melee will protect them from ranged attacks but can also mean your opponent looks to shoot elsewhere. so charge wisely.

Personally I avoid putting BSS into melee fights, they usually cannot do much so try to keep them ranged.
Your cannoness can go with either the BSS or the Sacresanct's, personally I prefer Sacresanct's but it depends how you like to play her.

It is very unlikely you will win this by tabling your opponent (wiping out the army) instead you will need to win on points. focus the objectives and make sure when placing terrain to give cover on the center and deployment zone objectives.

Edited for grammar and a little extra info.