For me running the race regardless of how ever you seed the riders in numerical order is a must. It at least gives all spectators a good chance to work out who is doing what. The commentry is mostly about the front runners so a back marker doing well stands out to one and all .
As for the five second gap I think this is a good idea and the way to solve the time issue is to have two gates at the start an odd number and and even gate.  The starters could alternate the gates the riders leave from.  You would leave your gate 10 seconds after the last rider from your gate , or is that to simple ?