1. Browser would work, yes on a hosted FileMaker solution with the licenses you have already discovered.
2. IF they can respond with Excel, that can be imported into FileMaker. In fact you can send them Excel (from FM) in a way that makes response import to match whatever you need (question->answer) with keys.
there are ways to import from email, but that's more manual, unless you use a plug-in or web service to read the email directly. an attached Excel (or just .csv) would be still manual (to get to the document), but a little easier than parsing the body of email.