There are a bunch of different types of blades. The #11 blades are |/ shaped. Here's a link to what the shapes are https://www.preservationequipment.com/UserData/root/Products/Images/000529_0.jpg
The #3 handle fits #10-15 blades.
When I'm cutting using xacto or scalpel I end up holding it in such a way that the handle shape doesn't matter too much. I grip it so my palm goes over the top of the handle and the top point of the handle presses into the back of my palm so that I have more leverage to make the cut. I find if I hold it normally it is very hard to actually cut through the material, but that could just be me.
Wow this is REALLY detailed. Ive been thinking about getting into foam for some time, not necessarily for Halo armor but other projects. I dont suppose youre going to assemble a Pdf version are you?
Also only use this stuff in a very well ventilated area, and definitely avoid contact with your skin, or clothes, or furniture, or anything you don't want gluey. It is waterproof so IT WILL NOT WASH OFF.
Would you have a link to the solution for the glue so that we have a link ready before someone comes in and says "help, I've glued myself to my mate, how do we become unstuck?"