as 'flexible' as Drupal is, I find the same lack of 'real world' examples for anything but the simplest matters ...
Generally I think of a module that does the same thing and then look to their code, for a huge multi-step form, have a look at node_import
"If you come from a background where you have created your own forms directly in HTML, you may find Drupal's approach a bit baffling at first."
Yes but the XSS, CSRF, session mgmt, user mgmt, permission mgmt and so on and so on benefits make it worth the time.
In DIY HTML/PHP, 'this' is all trivial.
Yes but see previous point, getting 'this' with 'those' features done properly is not trivial
Building a non-standard workflow around core forms, using Drupal internals and 3rd party module extension is ... a bit challenging.
Yes you are jumping in at the deep end
Trying to contact the developers whose modules I'm trying to understand/extend has been less than fruitful, receiving a sometimes cool reception ... though I _have_ received offers to take my money for paid consulting ;-)
Well in general with custom requirements you can have it now or you can have it free, but rarely both