Could you explain in a little more detail your problem. The creation of a predecessor or sucessor is completely independent of the item to which the last work order is related, so where, exactly are you having the difficulty.
To add to this, why don't the workorders/pred-succ's show up in the pred/succ's tab?
Do all pred/succ need to be set up as a template initially? before being used as such?
How or rather can servicedesk pred-succ workorders be set up to only be editable when the pred/succ has been completed? otherwise I see you cant edit status, but that still leaves a bit to guess work as to which order the work orders need be completed.