Hi,
I don't have time right now, and will be AFK for a day or two, so just some $subject:
1. handle_integer_setting() uses gboolean *setting. It works, because gboolean is actually int, but I think that should be gint *.
2. ui_editable_insert_text_callback() checks only the first character (assuming typing?), so you can, say, paste 1boza in Go to line. GeanyInsertNum contains a callback with full check, similar what is required +-number.
3. It would be nice to have the Document -> Indent Width -> # commands bindable to keys. Personally I don't use Ctrl+# for sending selection to custom commands...
Ciao for now.