By "Tunes", I assume that we're referring to "instrumentals"?
Are "Songs" a capella vocals?

I have been trying to sort of alternate between the two; since it's kind of hard to sing while playing flute or whistle, I do a medley, or an instrumental (sort of expecting anyone who knows the related lyrics to pitch right in) - or as is the case with "Strike The Bell", lead off with the whistle to get things going, then sing the rest (I suppose that would be "leading") a cappella.

Am I violating any traditions or protocols by doing that?

For all intents an puposes, these Chanty Sings have been my first significant exposure to the "Folk Session" experience, and I'm probably guessing at what most participants consider second nature.
If I step on anybodys' toes in one, I hope you know that it's not intentional, and I'm open to discrete, corrective feedback.

Is a song accompanied by a guitar, banjo, concertina etc. considered a "song" or a "tune"?

If we are supposed to be concentrating on a capella vocals, would it be best if I were to just leave the instruments home?

The implication here seems to be that factions have evolved around respective presentations - sort of like Street gangs.
Instead of "Blood" or "Cryps", we have the "Tuners" and "Singers", eh? Did I miss any?
Are we supposed to join one and eschew the other, or is a certain modicum of crossover tolerated?

When it comes to this social etiquitte stuff, my New Hampshire hillbilly upbringing sure shows up, and I rarely seem to have a clue.

Has anyone ever published a standard list of rules for the Folk Session for rubes like me? Is it somewhere here in the MC Archives or any other web site?

whatever gaffes I have committed (and I'm sure that there have been legions of them) folks at the Chanty Hoots have been most gracious in forgiving me, and I do appreciate that!

Our life is in a bit of a state of flux right now, so I can't say how many Sat.s I will be able to go to Portsmouth. Hopefully, there will be at least a few.
During the Summer I am often involved in Civil-war Reenacting on the weekends if I'm able.

Anyone coming South through Yarmouth and open to ride-sharing do let me know, as I'm not only all for being reasonably kind to the Environment and optimizing urban parking spaces, but would love such an opportunity to get to know a fellow 'Catter a little better, and perhaps noodle around with some vocal harmony enroute.

We'll stay tuned for furthur developments.