How long for the tie?

[Downunder Kilt]

And if your not wearing a vest then long enough so that its almost touching the top of your kilt/ belt buckle.

This is what I go for also. I have my old school ties and work associated ties that are ideal for kilt wear. ie they are not the wide flared type. I often wear the ABF tie and have never received comments that it looks too wide. I always use the schoolboy knot in preference to other types