Very nice image Paul.
Re the out-of-round stars: This looks to me like a tilt problem.
Fast Newtonians are extremely tricky to align, and axial collimation alone does not guarantee good performance across a camera field of view. There are two approaches: one is to install a tilt corrector - often not possible because of the short backfocus.
The other is to play with the secondary position along the primary axis. I know from experience that this is extremely tedious and time-consuming.......but you probably knew this anyway
Forgive me if this is redundant info.....
Mark