Well, I'm reading Keith Richards' autobiography right now and no less an authority than the man himself strongly, strongly advocates learning on an acoustic before graduating to electric and I'd tend to agree. There's no hiding mistakes on an acoustic and if you want everything to ring out right, which you probably want to do around a campfire, you'll be playing on an acoustic anyway.
As to the sort of general question I think a lot of it depends on how much musical knowledge you have going into it. When I learned, guitar was my first instrument so having actual instruction from someone who taught me a little bit of the ins and outs and tricks of the trade was pretty valuable.
That said, it's not entirely necessary if all you want to do is strum out some sing-alongs. My advice would be to just find a chord chart(something like this
http://www.chordie.com/chords.php but any place that sells sheet music will sell an offline one for cheap) and memorize the major chords and just practice switching between them. Once you've got a good idea of what an A chord is and how to play it, what a B is and how to play it, etc then as you say there are lots of sites that will list songs, their chords and when to make the changes. Play along with songs to get the timing and you should be able to play at the level you're aiming for fairly quickly. You'll be limited by your memorization as opposed to learning things by ear but that's something you can learn as you go.