How do you recommend to create a field for Comments or Notes in a feature class?
as a text field? What will be the maximum size?
I think this will all depend on what information you are putting in. Maybe keep it to under 255 characters if you want to export it to a shapefile or so (since that is about the max length of a shapefile text field).
This link will give you some info on file geodatabase size limits:
File geodatabase size and name limits—Help | ArcGIS for Desktop
Maximum length for text field is :
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