On repertoire - make it as eclectic as you dare, if the folk police are testing your Scottishness - try subterfuge.
Eric Bogle songs for instance. Consult the history of folk and link any to Scotland via the findings of researchers (eg Child Ballads) and you could even play tricks on the incredulous like linking "Molly Malone" to the first known publishing of that song and accreditation to a Scot in Edinburgh (search the 'Cat - it is here because I asked the question years ago). If you have a co-operative audience of uni students they will relish the game.

At the Somers (Malvern/Worcester) we had nights like that, tenuous or genuine connections to a given theme. It livens the proceedings and gives it a certain piquance.