What is the min.number of strands of fast flight for 50 lbs. Can a skinny be made from this material?

Leonard, I would try 12 strands if it were me.
You could go down to 10 or even 8, but I don't feel it would benefit anymore preformance.

I like f.f. but not big on skinny, like alittle meat with my potatoes!

Love that Mulie you have there.

Good shootin, Steve

I use 8 strand D97 or use a 6 strand 450+ for 50# and under.They have been holding up fine and working great.I do double serve for the nock fit I like.I serve first with .018 and then .021,this gives me great fit for Easton 3D Super nocks and large groove G-nocks.

I have been shooting a 10 FF with padded loops on a 63# Thunderhorn Heartstopper for the last 9 months. Probally have somewhere between 4000 and 4500 shots from it with no problems.  I only dbl. serve in about a 2 inch area for the nocking point. Doing a test shooting fingers I gained almost 7 feet a second going from a 16 strand FF.
For your bow a 8 strand would be just fine.

On my 56# bow I found I lost preformance with a 8 strand D-97 verses a 12 strand, but that is just on D-97 which is all I have.

I use 6 strand D97 flemish on a 46# bow, with a definite gain in performance!

I'm shooting a 6 strand 450+ with 12 strands in the loops on a 1967 Shakespeare Necedah.  I've probably shot over 2000 arrows through it with that setup and it's much more dead in the hand; literally no vibration through the limbs into the riser.  It is much faster than with dacron, but the biggest up side that I see is the lack of after-shock/vibration that is normal with dacron.  

And yes, I know the old bows aren't supposed to tolerate the fastflight material, but I have two old ones that like it very much and actually show much less vibration with the new string material.

I am shooting a 12 strand FF on my 59# @ 29", R/D longbow. I have only been shooting it for a few weeks, but I love it. Much quieter than my 16 strander. I would think you should be able to go with a 10 strand without any problems, been thinking of making one for myself.