Expansion modules

[ORSO2001]

Dear All,

at the moment I am working on a project that include 7" HMI + CPU and  21 IN and 15 OUT (relay); these I/O modules will be localy fixed in the rear of the OPLC (as usual); in the next future the I/O will has to increas x6 (at the end 147 (21+126) IN and 105 (15 + 90) OUT)...these next I/O modules will has to be installed in an external box 3 meters far from the OPLC location.  My questions are:

What I have to consider about the hardware (cable wiring and power supply)? 

which components I have to acquire?

thanks