Sissor-type moulds with sprue cuttoffs usually had them on the handle end of the hinge pin of the mould handles.

The rifling twist will dictate how long you can make the 'sprue'.
Attaching wads to it, might be a good idea - or not. Testing will tell that story.
Still looks like a 'typical' American picket-type bullet to me.

Yes- the addition of wads would help centre the bullet.
What is the diameter of the inside cavity of the mould? Subtract about .002" for actual bullet size in soft lead, which is probably correct for the gun. Hardened lead makes loading more difficult to impossible in a muzzleloader and will eliminate the bullet's ability to obturate to help seal the bore.

The sprue cutters normally cut the sprue off square with the base or nose of the bullet.