Would the affix template you suggested work for this word?

1. Suffixes themselves are treated as lemmas in their own right, and use the category "suffixes". For non-lemma forms of suffixes themselves, there's the "suffix forms" category.
2. Yes you shouldn't remove the poscatboiler templates or similar templates. But you're right that maybe the text could be reworded. Instead of "located at the end" it should say "added to the end", which is more correct I imagine? The text itself is located at Module:category tree/poscatboiler/data/lemmas if you want to modify it yourself.
3. We have separate categories for circumfixes, like the English one which has an entry at em- -en (so just the prefix and the suffix with a space between) which is located in Category:English circumfixes. And there's also the category Category:English words circumfixed with em- -en, and its parent category Category:English words by circumfix. So as you can see it's very much the same as with prefixes and suffixes. You can't use the {{affix}} template that I showed you for these though, because it's not able to tell when a prefix and a suffix should be seen as one whole. So instead there's another template {{circumfix}} which would be used in this case. It is used like this (with embolden as an example): {{circumfix|em|bold|en|lang=en}}.
4. It's a bit less typing because you don't have to type the parameter names t= and lang=. That's about all, but it is also more esthetically pleasing because having the language code first matches how {{l}} and {{m}} work too.

And you're fine, I don't mind answering these questions at all.

RE: The text itself is located at Module:category tree/poscatboiler/data/lemmas if you want to modify it yourself. I am concerned that if I did that, it might affect other people. I wouldn't want to change something that they are also using. So I just added an explanation to the page after the postcatboiler text.

That page contains the information for various categories, such as which parent they should go in and what description to show. If it's changed, several categories would be affected, but in this case I think that's for the better. I've made the change myself now, you can see what I did. Note that now, Category:Wauja suffixes has a different description, but so do Category:English suffixes, Category:German suffixes and so on. This is why this templated category system is useful; it allows all the categories to be changed simultaneously from one central location.