Hiya Sashisruski,
I'm going for DEO pilot but will try to answer your questions in any case. I'm still in the application process as well so I'm not an expert - feel free to disregard my advice!
1. It's really up to you as to whether you want to pay to undertake the first part of a uni course that you would essentially repeat were you to get into ADFA. Personally I would suggest that ADFA is the better option rather than an external degree if you really want to be an ADF pilot. You will be exposed to the military lifestyle, be paid to study instead of accumulating a big HELP debt (like myself), meet many other aspiring young ADF officers etc. The alternative is to undertake an external degree like what I did; this allows more flexibility, ability to travel overseas, etc. I think this was probably the best option for me as I don't think I was ready to go to ADFA straight out of high school. I now have that extra bit of life experience that I wouldn't have accumulated otherwise - but we'll see if that flies at OSB if I get a flight screening spot!
Another option could be to work to fund flying time while you wait for your ADFA application to be processed?
2. Once you are on Pilots' Course your prior education should not be taken into account. There will be students there who have no tertiary education whatsoever whilst others might have PhDs in astrophysics - as far as I'm aware the course is the same for everyone. Obviously your AvTech degree will give you a bit of an advantage over others initially - my degree is in economics for example so I doubt whether that's going to help me much in the cockpit.
Hope this helps a little - good luck with it all mate,
Jimmy