First floor bathroom / bathroom en-suite wastes

[Rishard]

Hello, just scouring the web / forum for similar ideas relating to first floor waste runs. I’m trying to work out the best way to route my waste pipes back to my stack. 
 

Is it best to try group the en-suite shower/basin/w/c into one 110mm pipe and back to the stack, or keep w/c separate from the basin and shower? From my research, these could step up to 50mm pipe from the basin/shower and back to the stack. 
 

OR 

 

Should I be trying to group say the w/c from the en-suite and the bathroom on the same 110mm run to the stack? Keeping the en-suite basin / shower on one 50mm run and do the same for the bathroom? 
 

I have posijoists which I can route most of these runs in. The w/c near my stack could go through the wall if beneficial. 
 

I’d also take some advice on good way to fix all this pipework to the posi joists. I thought about using some rips of ply to use as a side wall which I could clip / fix pipes to (on a fall) but if there are any other good bracket fixings people have used which would take up less space I’d be interested to know. 
 

Has anyone used much dampening on the larger soil pipes to reduce noise? Just a thought as the stack is currently coming up in the corner of a bedroom. This could be adjusted to come up in the bathroom if it makes more sense. 
 

Thanks for any insights. 
 

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