Good Q's !
Conductor arrangement is not finalised as I am trying to make it modular.
In reality, there maybe a 12meter loop with 4 sensors; and 2 spurs with 1-2 sensors each, 1 of 4 meter, the other of 2 meter.
I'll work in parallel where possible.
Current: for each sensor I am expecting .120ma with peak .200ma (no data sheet - working of other user's comments until I can measure for myself)
Arduino location will not significantly add to the distances mentioned above, 0.5m maxmum.
Cable will be routed along a mixture of terrain : along walls, behind strips of wood; and buried if possible.
From your cable suggestion, I guess I ought to add the complexity of wiring in parallel.
If I have 4 PIRs on a loop, I'll need 4 signal wires + 2 power lines.
Had I been doing this indoors, I'd probably have used 2 power lines on a ring/spur, and 1 ribbon per PIR to send back the signal.
Leaving things open for expansion, I could go with 2 power + 6 signal.
On the other hand, I'm sure this has been done before ... so open to advise.