1) Incendiary head arrows are all I could find, too, so your GM will need to extrapolate from there I suppose. SR4 actually had white phosphorus grenades.
2) The expression of magic is still unpredictable/a mystery, although corporations and others are still attempting to "breed" them. A magical couple expecting their child to be awakened is well within the realm of plausibility, though.
3) Mundanes who could create spell formulas used to a thing, but in SR5, arcana, like other magical skills, requires a Magic rating to use. I would just give the character a knowledge skill of magical theory to represent a mundane expected to awaken. No actual spell design, though, sorry.