You old cables served you well for this long. Why not use the same or stuff similar to what they used. Though Athena was from way back in 1990's or even late 80's isn't it? Not much has changed, cables got thinner at some point. Don't know if that was before or after your Athena.
Don't over think it. It's just a bike. If Campagnolo has a good support website with manuals and instructions for their individual components then consider their recommendations. Park Tool has a good bit of information on stuff. I've never watched any of their stuff on cables though. Sometimes their horsing around gets annoying. But their info always seems to be correct.
https://www.parktool.com/en-us/blog/...le+replacement.
And depending on what type of bike shops you have locally and their attitudes, you can come up with a lot of good info just jawing with them if you visit. Sometimes they are so lonely and in need of conversation, it's hard to get away once you get them talking. And many old shops will have bins full of ferrules of all types and cable stops that they've accumulated through out the years. Maybe they'll look through them and give you the one you need if it didn't come already with your set of replacement cables.
I used both plastic and metal ferrules on my previous bike. Plastic vs metal isn't as important as which one fits and is proper for the purpose where it's used at that cable point on the bike.