Alexis, thanks so much for your comment! I spend a lot of time on foreign websites and talk to natives to learn the differences between cultures. Unfortunately, there are no shortcuts.
If you really don't want the traffic, why not use geolocation logic that sends users from non-focus countries to another page?
Chris, thanks for your comment! Rel-alternate is only necessary when you target individual countries with translated content. The easiest way to internationalize and what I would suggest for anyone getting started on global SEO is to just do language level targeting.
For example, your Spanish language content will target every country that speaks Spanish. Google can recognize the language, and doesn't really need the HREFLang to know to serve Spanish pages to Spanish queries.
That's a really great idea! When it comes to internationalization, I always try to put myself in the user's shoes. Would I buy a product from a foreign language site if I couldn't understand the site well enough? Probably not. Anything you can do to create a connection, even if it's as small as country flag, can increase user comfort with your site and lead to a increased likelihood to convert.