You have not missed anything obvious in the User Guide- the way I approach this is search online for how it's done in Adobe, since that's where all the examples and tutorials are. As long as you stick to AcroForms things, you should be good.
Here's a great example on how to do at least your second thing: https://acrobatusers.com/tutorials/js_disabling_fields
For the first thing, this might work for you: https://forums.adobe.com/thread/1877008