Q) Why do you have to have the line behind the float?
A) With the line behind the float, the flow of the river presents the bait more naturally, so I am told
Q) When you strike do you trap the line and then strike ?
A) I do... purely because it's less slack to take up
Q) Do you have to use a stick float ?
A) No... I use a variety of floats dependent upon the conditions, but a stick float is more direct in its indication, which is, after all, what the float is used for
Q) Do you let line off of the spool when the float travels downstream ?
A) I allow the flow of the water to take the line and I mend as necessary. I use a finger on the drum for control when I think I need to!
As for the amount of line on a 'pin, I have about 50 yards of 4lb mono and either fish 'straight through' or a 2lb hook length. I have neen reasonably successful either way, and after the first couple of sessions seem to have lost the skill of tangling myself up!
I am open to correction on any of these points, but they are based upon what I have read and practiced.
All the best, Alan