question on speedfit water pipes

[larold]

In my upstairs bathroom and ensuite, I want to ultimately supply water to a bath, 2 showers, 2 washbasins and 2 WCs. Does it matter where I tap into the pipes to feed each thing? Do I have to always feed off the main pipe and run directly to each thing or can I feed off a pipe which is already feeding off the main pipe (if you get what I mean).
The hot main pipe seems to be 15mm and all the feeders are 15mm, but the cold looks more complicated. The main seems to be 28mm, then at present there is a 22mm feeding off this, then individual 15mms feeding off this to bath and sink. Which one do I feed off for the extra shower etc? Does it make a difference re water flow/pressure?

 

[neds]

Will make no difference really, If its a combi then obviously the flow will be affected when other taps in the house are turned on. To your original question, T off wherever you like.