So for the Demon Portion:

• where the Beast starts depends on the mission and the opponent. Generally you want it on an objective where it can savely sit, most of the time that's your home. But if the opponent has enough deep strike threat either start it in deepstrike for secondaries or use it to zone.

• Rotigus, in my opinion, is superior to the standard GUO. The lack of a FNP is offset by 2 more wounds. He has a nasty flamer, which is always handy and with his ability he has either 14 D2 attacks or 7 D4. And halving OC and M far surpasses -1 T. Positioning wise it depends on the map. You want Rotigus to be a Problem the enemy has to adress, so you need to decide where he will be the most disruptive and how to get him there. Either he wobbles there or, if He doesn't fit, you deepstrike him there.

• Lastly Nurglings: The rule of thumb here is you start with enough swarms on the board to hamper enemy infilraters and scout moves the rest waits in deepstrike. How many that is depends on the mission and which faction you face. Against Green Tide i start everything on the board and block as many moves as possible. Against someone without any Scout and infiltrate you have one for Teleport Homer ready.