Right now I am working on having a fixed version of the Bob Lum Chinese utility folder made, so I'll let you know after that comes in! Otherwise, I really like my Endura for everyday chores, as well as my Calypso. To me, a blade length of three-4 inches is more than sufficient for 95% of my everyday carry duties. I would probably be able to get away with a Sean perkins Kerver at 2" of blade, as well! Anyway, I haven't really formulated a preference for hollow or flat grind yet, although I like the looks of flat grind better. The knife should have a decent amount of belly, a nice sharp tip, and a relatively narrow width. I would say 1"-1.25" width with a spear or drop point is ideal.
A drop point, 4-4.5" blade, 5/16's" thick, with a flat grind (BG-42 or 440-V would suffice).
I, personally am not a fan of the false edge on the spine and plain edge is preferrable to partial or full serrations.
A drop point or any kind of utility style blade will do- it's your customers' personal preference. A 3' inch blade is probally the most pratical, being that that is the legal length of carry in most states. A smaller knife also allows for more options for carry. A 3'inch blade has enough length, and heft for average everyday use. 1/8 in stock, flat or hollow ground, and no false edge to make it look less menacing. A nice sheath with it will sell well.
A Knife is no more than an Iron Tooth
I think my favorite blade is the Benchmade Weehawk used on the 710 Axis lock. It has moderate belly, an aspect ratio of about 4 to 1, and a sharp, roughly centerline point. I would like it just as well without the recurve.
I don't like fixed blades myself, but my favorite blade would be a modified Tanto blade followed by a clip blade. Cutting length I like is 4" - 5". In a stainless steel, BG-42 would be number one followed by CPM-440V. Edge would have to be 50/50 or so. If I never wanted to worry about rust of chipping of the blade easily, then titanium for a blade would be great.