Why not use the IPTC instructions field?
Hm yeah I might use it.. problem is that you have to basically look for it.. I would prefer something like a description/comment section, dedicated
What are the possibilities here?
1. Use an existing field, e.g. EXIF or IPTC. I recommend the 'User Comment' field in EXIF (enable EXIF or 'EXIF & IPTC' metadata viewing preset to make field available).
Whatever you choose, if you don't want it exported, you can use Jeffrey Friedl's Metadata Wrangler plugin to block it (if your export/publish-service supports post-process actions - some don't).
2. Use Custom Metadata (a free plugin I wrote).
You can define whichever fields you want, and they won't generally be exported (not in the initially-exported image file anyway).
What do I recommend? - if one field is enough (e.g. free-form notes in Lightroom), pick a free exif or iptc field and use it. If you want to spread your various infos over multiple fields (for better organization, to take advantage of enumerated or url-link field types, and/or for external considerations..), use custom metadata plugin.
PS - consider using Jeffrey's Metadata Viewing Preset Editor to customize a view which includes your chosen fields.
Thanks for the detailed information Rob, I will try your recommendations