If you have 10 GC at 2 fids per GC all on at the same time using 40ml/min of H2, thats only 0.8litres per minute. I am not sure what the max would be, but I have seen that many GC on 1/8th inch line. The tricky part is when you get to the carrier gas and are running splits and carrier consumption is higher. I havent been involved on the gas system design of a lab so will be interested to hear what others have to say. I did add a few more tags to your post for better visibility. One item to note, make sure whoever is installing your gas systems uses tubing that has been cleaned for chromatographic use. I have seen some bad situations with incorrect tubing through the years.
I marked this assumed answered. 1/4 inch has line would be fine as long as its clean and free of oils.