
I just found out that australia and Austria have a bilateral agreement which means I can re-enter Austria after my 90 Schengen days are up, from the U.K. and get another 90 days stay in Austria!

But I’m a bit confused about some parts:
1) Do I need to use all my 90 schengen days (non-austrian) up before I can use my 90 bilateral days in Austria? I currently have 17 days left in Schengen zone on my UK passport, do I need to use them up first then fly back and forth to start my free 90 days or can I just start the free bilateral days from when I enter from the U.K. next week?
> If not, can I still use my remaining 17 days during the bilateral period. For example, if I spent May in Austria on the bilateral agreement, could I fly to London and then to Spain for 17 days and use the remained up?
2) Does the Bilateral agreement effectively make Austria like a non-Schengen country? Ie, The Austrian site says, the free 90 days are irrespective of the 90/180 rule. Does this mean when I’m in Austria on my free 90 days the clock is resetting on my other 90 days? Ie could I do 90 days Switzerland (90/180), 90 days Austria (free 90 days) and then 90 days in Switzerland (90/180) again, etc?
3) What do I need to do to apply the agreement, I believe I just need to enter from the UK with my Australian passport and have proof that I will be staying ONLY in Austria during the period? I will be staying with my girlfriend in Graz the entire time, so will a utility bill of hers be fine?
4) Can I use the 90 bilateral days and 90 Schengen days at any time, as long as they balance and as long as I always enter and exit to a non-schepgen country? For example, could I spend 50 days in Switzerland (Schengen days), fly to London for a few days then fly to Austria for 20 days (bilateral days), fly back to London for a few days, then fly to Spain for 40 days (Schengen), then fly to London for a few days, then fly to Austria for 70 days (bilateral days). This would effectively mean I’ve used 90 days in the Schengen zone and 90 days in Austria using the bilateral agreement over 180-odd days, which should be compliant, or can I only enter Austria once for up to 90 days?
5) How many times can I enter Austria, is it up to 90 days per year, twice a year, or can I literally spend 360 days in Austria as long as I leave on the 89th day each time?
Many thanks!!