Bob its kinda funny you mention how your group makes purchases by placing the unit on top of the stack of IPCs. I laugh because most of our group does the same thing. With that said you will need lots of singles. I counted up the average incomes for each power and figure you need somewhere around 300+ IPCs to get through a round in G40 so you definitely would need 2 sets from FMG IMO (each set has 200 IPCs).
I would add that although the IPC chip set from FMG looks really nice, I don’t think I would spend over 100.00 for 2 sets. I would just purchase a normal set of poker chips first to see if it works for your group (someone in your group probably has a set that you could try out). I haven’t used poker chips as IPCs but the poker set I own has 4 colors (white, red, blue, black) with 50 of each that would work very well for 1’s, 5’s, 10’s and 20’s (or 25’s). I really don’t think you need the denomination amount printed on the chips, you just need everyone to agree on a standard.