Pkay,
Some astrophotographers use auto focusers and this is the way to go however like you I'm still learning the ropes too. My Newtonian has been modified to enable photography and the setup isn't ideal. I find zooming in on the canon live view helps prior to locking it in. Sure atmospherics vary the focus during the session but not enough to bother me too much. I take 25-40" subs and even though the star roundness isn't perfect it can be remedied. Shorter exposures certainly help retain star colour rather than overexposing through longer subs. It's all trial and error, I find plenty of error but hey every new trick goes into the melting pot.
