I have always found learning (and thus teaching) is better achieved when new concepts are introduced incrementally. I would suggest, in the first instance, teaching the basics of triads as based on a major scale. Then triads based on a minor scale (for simplicity, probably best to choose the relative minor of the previously-studied major!). I would hope any enthusiastic student would be happy till this point. Now point out that, given the selection of notes we have been using, these two scales are just two of the possible scales available to us: now introduce the others, one by one, and build triads upon them.
I think there's a tendency in formal music education to concentrate on major and minor scales and more or less ignore modes, and for that reason when a student comes upon them they tend to think of them as difficult or even scary. I agree with your thinking: introducing them fairly early on, and emphasising that the major and minor scales are just modes like any other, is a very good idea.
A couple of good explanations of modes can be found at:-