It would be nice if there were fields that are required to be filled out when e-signing a document. Such as... name and ages of all guests, breed (and name) of dog(s), etc.
Yep, we actually do support that now on signing links. Any field on the contact page of the quote checkout is also required when e-signing a document, including booking custom fields flagged for checkout: https://www.ownerreservations.com/support/articles/capture-additional-fields-on-checkout-quote-acceptance -- we sort of stealth added that a month or two ago and haven't fully announced it.
We don't have a dedicated guest list field, but you can either do a rich text custom field with a description that asks for name and age of each guest one per line, or you can add multiple fields, one for each name.