Interdependancy visa from working visa help req'd

Hi folks, I used this group for info when coming to Oz and found it very helpful. I now have a few questions i'd appreciate some advice with if some kind person wouldnt mind answering.

I'll tell my story first. I came to Oz in January on a years working holiday visa. The reason i came was to see my Girlfriend who is an Aussie and lives here. We have now decided that i'd like to stay in Australia and believe the best option for this is to apply for an Interdependancy visa?

We have been together since October 2004, although in terms of actual time spent together we have spent 4 months living together in scotland , and so far have spent 6 1-2 months living together in Australia. So by the time my working visa expired we would have 16 months of time spent living together.

Basically I would appreciate any advice about applying to stay, Especially from anyone who has been in the same boat. These are my main questions:

Is the interdependancy Visa the best choice for me?

What kind of Information would I be expected to provide (letters etc as proof of living together?)

Where should i start (what forms, etc)and when would be the most beneficial time to apply.

And a big question is, I'm planning to travel back to scotland for 3 weeks in October. Does my Working Holiday visa permit re-entry? Someone also told me that once you apply for the interdependancy visa you are not allowed to leave the country until its granted, Is this true.

Apologies for so many questions. Any advice-help would be greatly appreciated.

Thanks Paul.