Sounds like some of the bigger Bass bashes and also the events run in Manchester by Stevie Williams a few years before the London Bass Guitar Shows.
1. Yes, I had Scott Devine and Geoff give a masterclass at a Yorkshire Bass Bash many years ago before he was on YT. That was interesting and would be even more popular now too.
2. Workshops are well attended at the LBGS, let's face it anything to get away from all those slappers... the SE Bass Bash has had such luminaries as Herbie Flowers, John Bentley and Mo Foster I think. There are plenty of celeb Bassists in Scotland: Ewen Vernal,Johnny McElhone etc etc who may be interested
3. I expect Alan Cringdean from Moffat could be interested, it may be a bit hard getting some of the Southern Luthiers up there. Alan came down to a Yorkshire Bass Bash too.
4.You need to steer clear of other euro events and Namm to get the big makers along, we had the Northern rep from Markbass when it was with Proel at the YBB.
5. You'll need to sell a lot of tickets to get some of the bigger names along, if they are touring nearby it could help. I remember seeing Poogie Bell in Manchester, the venue was also the Music College so they piggybacked onto who was visiting.
6. I know the Manchester and London Shows were/are months in the planning and are run as a commercial venture with fees for stands etc etc.
You may wish to set up a Scottish Bass Bash first to test the water, there is lots of info in this Lounge from those who have run Bashes. Good Luck!