IMHO the books you have ordered are enough without the Bill Scull one.
For more advanced work, i.e. cross country and competitions, books by Helmut Reichmann (Cross Country Soaring) and George Moffat (Winning on the Wind) are well regarded. These are nothing to do with how to handle the controls - which you will easily adapt to with your experience - but the techniques of finding lift, maximising speed round a task, etc., which are different and specialised skills compared with other sorts of flying.