I'll try to see if I can find something better. Stay tuned...

You should call Adobe customer service.

The code is in the file, most of it in document-level JavaScripts. The same thing won't work with LiveCycle Designer form, but there is a forum for it where you should ask about what's possible: LiveCycle Designer

There is no type of check box that behaves that way. You can fake it using buttons and JavaScript, as demonstrated in the following sample: http://acroscript.net/pdf/demos/multistate_4.pdfYou'll have to study it to see how it works. Note that you can only rely on this technique working with the desk...

You don't need Acrobat, your client does. It's far less cost than LiveCycle Reader Extensions, which would have been the only option before Acrobat DC was available. Licensing costs can be as low as $14.99/month. So if their need is limited, it can be done for very little.

You can't use Reader, you have to use Acrobat. So your client will have to get Acrobat and Reader-enable the forms that you develop. If you don't have Acrobat, you can download and install the trial version so you can test this out.

Open the form in Acrobat DC and select: File > Save as Other > Reader Extended PDF > Enable More Tools

An option is to Reader-enable the form with Acrobat DC. It doesn't have the licensing restrictions related to enabled documents that previous versions do. You won't be able to Reader-enable documents for your client with Acrobat, but your client can.

OK, so you're pretty much limited to using form fields, something like a grid of check boxes.

Reader-extending doesn't disallow commenting, rather the opposite. But a dynamic XFA form won't allow commenting. Is your form static or dynamic? If it's dynamic, does it need to be?