I am building a script font with .fini alternates for the ends of sentences and/or for words used in titles. They’re not appropriate for mid-sentence. Should I recode these as .ss01 alternates or is there a way of preventing them from appearing when followed by another letter or a space?
There is a way. See the Positional Alternates tutorial:
https://glyphsapp.com/tutorials/features-part-4-positional-alternates
What’s important is the ignore statement. And the scope of the AllLetters class you use for the context.