Yeah true it's more then one chord but for simplicity it's pretty much the same grip for the majority of 'em. As for the strain everything you try on the guitar hurts the first week especially on steel strings. You're fingers tops will loose slight sensitivity. strain from chords you're shoulders might even cramp from holding the darn thing the wrong way.
Generally start learning some basic notes and chords. Power chords would probably strain your hand too much at first and be harder to play. Plus a power chord isn't just 1 chord, there's quite a lot of 'em.
nah you could still do a lot of variation with those such as muted palm. Besides that it's an easy way to start if you're too lazy to learn the basic ABCDEFG chords
Oh and a rock song made of power chords only would be awful,
and booze makes it much harder to play at first.. but you can get used to it!