First, about El Mariachi... It was filmed almost 20 years ago and was one of the films that started the current micro-budget indie film trend. It also had a lot of good things going for it to compensate for the sound quality. Sound was captured on set but so poorly that ADR had to be done to obtain dialog quality. (BTW, get the terminology correct; ADR is the actor replacing his/her own unusable production dialog due to on-set technical problems, dubbing is replacing the original language with another language.) Anecdotally - I've heard from peers that the ADR sessions on El Mariachi were extremely long and "painful".
I was drafted onto my first production sound gig. On a lark I showed up to be an extra on a short film and, because of my audio knowledge, was asked to be production sound mixer. I had lots of recording studio experience, so I already knew about signal flow, levels and gain-staging, etc.
You're going to have to interview a bunch of guys and trust to your instincts about their knowledge; you'll have to separate the ones who know what they're doing from the BS artists. When it comes to using a laptop to record production sound it depends upon what type of audio interface is used - crappy interface = noisy sound, good interface = good sound. Many PSMs use Boom Recorder on their laptop (
http://boom-recorder.en.softonic.com/mac). The biggest thing to keep in mind is that a laptop is not very mobile; indie film does a lot of run-and-gun, so most one-man-band production sound guys wear their entire kit while booming; you can't do that with a laptop, that's why a unit like the PMD-661 or FR2-LE (or Zaxcom Deva or Sound Devices) is used.
Like I've said before, get out there and work on other peoples projects; you'll learn a lot and make contacts for you own projects.