oh boy, you certainly did your research and dove straight in to the deep end
. One important question, do you have guiding set up? without it might be difficult to get longer exposures on your SCT (might be easier with the hyperstar but still useful). If you dont have guiding right now than you dont need to worry about PHD2 (guiding software). I'm not too familiar with celestron mounts but the software that comes with the mount should be fine (assuming you have the right usb cable to connect the mount to computer). No, you don't need two computers. I think in terms of software youd need an image capturing software like sharpcap or other similar softwares (theres several aha), guiding software PHD2, post processing software (Photoshop, GIMP or Startools or whatever you're most experienced with).
I see that you're in Gold Coast, this post wouldn't be complete without plugging our local astronomy club SAS. Theres a monthly meetup where you can talk to more experienced people that can give you feedback face to face.