Multiple glyphs of warding can't ward the same thing...
The target of the glyph of warding is listed as object touched or up to 5 sq. ft./level, and the spell's description says
Multiple glyphs cannot be cast on the same area. However, if a cabinet has three different drawers, each can be separately warded.
This prevents chained glyphs exactly as you describe, and for good reason. For example, were multiple glyphs able to ward a lone tiny box, triggering them all simultaneously creates disastrous consequences for the approaching army—seriously, a tiny box will be picked by someone and opened (especially if it's a shiny box), and if there are hundreds of glyphs of warding on that tiny box then boom—goodbye, army. (To actually run such a trick, try the spell explosive runes instead.)
...And a touch spell stored in a glyph of warding will affect the creature that triggers the glyph
The spell's description says
You can store any harmful spell of 3rd level or lower that you know. All level-dependent features of the spell are based on your caster level at the time of casting the glyph. If the spell has a target, it targets the intruder.
Emphasis mine. The spell touch of idiocy has as its target living creature touched, so a living creature triggering a glyph storing touch of idiocy will be the target of the spell despite the spell's typical casting method. (By the way, multiple penalties from multiple touches of idiocy—as they're from the same source—shouldn't stack, but ask the DM; a penalty is a little more complicated than a bonus, despite the lengths of those linked entries.)
Although the text isn't specific, it's safe to assume that summoned creatures from a spell glyph aren't random creatures from the summon monster list and instead chosen by the glyph's creator when the glyph is created. Likewise, a suggestion spell held in glyph should offer a suggestion that the caster chooses upon creating the glyph rather than offering a suggestion of the caster's choosing when the glyph is activated.
That said, this is a really expensive way to secure a wagon
A heavy wagon only costs 100 gp. Spending hundreds of gp to protect it is an unusual use of resources. If available, consider hiring some locals to guard it. They'll be thankful for the generous 1 gp per day that you pay them to guard your wagon.