Drop the sheild on the venom, if it gets hit it goes down. There is no point trying to change the inevitable. If they get a free shot at it, then you have put it in the wrong place. Get rid of it and you can afford an extra trouper
Against white scars, who will use alot of bikers, you will be about even in number, but be wounding on a 6. Power weapons are really wased here so use a Kiss. I think I did the math correctly and a kiss and a power weapon come out the same when attacking a normal marine. so when your faceing bikes, it's kisses, when your facing termi's power weapons
If your fighting marines, dread masks are usually a waste, caue you can't run them down. If you decide to take them anyway, assult, and if you are sure they will run,
([like it's a small squad, like bikers have] with a leadership of 8 on the bikers you automatically make it 7 with "Mask of fear" then if they take enough casulties it's down to 6, then if you outnumber him it's down to 5.)
you beat them in close but don't use you tangle foot granades, this is because in the movement phase you have phase fielded a Djester in behind them and you will get cross fire.
While the SSeer might be wysiwyg (I assume that from the weapons you gave him) he just doesn't have enough attacks to ensure a 6 being rolled. give him a HK, PB and another close in weapon and you can chose between power or wounding on 2
stick a Djester in the venom. Make the Sseer part of the troupe, making a total of 6 harlequins, and then the independent character is free for the djester. It makes the crossfire method I talked about easier to acheive.
Hope this helps