I agree with Jeanne on the software choices.
Although I have seen very rudimentary ezines done in Word and then published to PDF and/or printed out.
As to setting it up for download once it's paid for the easiest way (non-coding) would be to have a Paypal button on your site and just email it to them once they've paid.
Otherwise, you'll definitely need someone who knows how to code to set up an auto-reply system (in concert with Paypal) which will generate a new link that's valid for X hours after payment each time (to avoid non-paying people jumping in there as well).
We've done this for a few clients and I certainly couldn't have managed the coding without my business partner/husband