RH is always your best bet. Then your spindle is running the right way, forward. The pressure on the turret is the same either way, its mounted on a rotary coupler so the force is always taken by the turret nothing else. Also most turrets your hard pocket (surface tool locates from) is for RH. If you use LH then your cutting pressure is on your tightening screws. As for the window upgrade your material used if it is an issue.