I don't think you can ever have too light a gripper. I think Chez starts light in his warmups, with a .5 or 1. I start every time with the Trainer (Chez's) and if he asks for it back I will have to replace it immediately.
Thus, I would say the first three grippers in any series is going to be useful to begin for anyone. For instance, a Coc 5., 1, 1.5 or maybe a 2, a GHP 3,4, & 5. If the person can close the Coc 2 or the GHP 5, he simply knows where he is and can buy a heavier gripper a step or two up. Most people are going to take at least a little while to be dominating the GHP 5 or the #2, and the lighter ones are still going to be useful.
The other thing to consider is that a Cannon rated gripper has high resale value in every range. Every time I have put one up for sale on the GB, looking to upgrade to a higher range, it has been gone in 24 hours, so one really need not worry about it.
Just my 2 cents.