how many disc ?

have an 09 HD FLHT with 103 kit & 255 cams, wimmer air cleaner & power commander with an auto tunner, Installed 2:1 supper trapps, not carrying about sound. How many disc should I use to get the most accereration/torque.
I almost always shift before 4K RPMS
thanks

17-20 discs with the closed end cap should provide the low end torque you're looking for.

should i start at 17 or start at 20 & is it going to be based on "seat of the pants". Based on experiences which should be best ?

We can provide a range of tuning; however we have NOT tested a motor with your specific mods.
More discs will provide more flow and potentially more top end ... your fuel management system should provide the correct A/F ratio to take advantage of that flow.