As far as using Amazon for migration to the web-serial, there is some validity there. My audience has grown substantially since I started my ventures into the e-book market. However, there are some serious hurdles in the way of using it just to gain serial awareness.
1) Chrysalis touched on this, but it really bears repeating: There are tons of free books on Amazon. Getting visibility is a major task for most authors. There are entire forums dedicating to tactics that might help to move even a few more copies a month, because it is highly competitive and saturated. People spends lot of cash advertising to get seen on Amazon, so in terms of getting eyes on your work its not a solution in itself.
2) The biggest and best tool new authors use to get seen is unavailable to you. Kindle Unlimited, or KU, allows people who pay the subscription fee to read all books enrolled in the program for no extra cash, while compensating the authors per page read. This is also the only way to do promos (I know you said permafree, I'll touch on that next) which is how you can use services like Bookbub. But, and this is a huge but, KU demands exclusivity. Your story, save for a small sample, can't be anywhere else on the web. That's why I had to take SP: Year 1 down for a few months in order to do promo work. Not really an option if you're trying to drive traffic to your serial in the first place.
3) Being permafree is not easy. Amazon despises that status, and you cannot set your book to be free. The only way to do it is to set the book to $0.99, list it on other retailers as free, and then have fans or friends report the lower price so that Amazon will price match it. This needs to be a constant process, as otherwise it will jump back to a pay book. It is worth noting that Barnes and Noble just allowed the Nook store to have books set to free, but given their market share of e-books you're not really upping your chances of being seen by that much. Still, it might make shoving Amazon's price down easier, so it's worth a mention.
4) This one is more subjective than the others, but I do think it needs to be said: lots of people are committed to their medium in terms of reading. I'll get a few e-mail a week asking when Year 4 is coming out, and when I tell them that they can read the first hundred plus chapters for free right now, the over-whelming majority say a polite "Thanks, but I'd rather wait until its done". That's not always the case, you are right that some people would read a serial if they knew it existed, just be aware that the conversion of ebook reader to serial reader isn't a huge percentage.
Not trying to discourage the idea, I think you might see some results if you've got the time to really push through all these hurdles, but I wanted you to know what sort of challenge you're in for.