But specific at least....
Firstly, I think I have things lined up fairly well, the secondary is roughly in the centre of the focusser, the primary is fully visible (roughly in the centre of the secondary) and using a Cheshire eyepiece the circle on the centre of the primary is dead on the central dot viewable through the Cheshire. However, In the reflection of the secondary I can see the edge of the focusser that faces into the tube and it's not central in the secondary reflection. I can see the whole of the focusser edge though. Does it matter and what is slightly out?
Secondly, when viewing a star at high magnification it has always looked like the atmospheric turbulence example here:
http://www.skywatchertelescope.net/EducationST.html
(bearing in mind that the scope is new and I've only used it maybe 8 -10 times so far). I've never seen the 'airy disc'. I had assumed that it was limitations of the scope, but now I'm guessing it is the 'seeing'. Where I live we have beautiful dark skies, but the diurnal temperature range is very rarely less than 15 deg C, often more (even in winter). Am I really suffering from atmospheric turbulence? Will it always be so with the diurnal temp range? What time of night is the best seeing?