How many amps can this breakers box provide?
is this setup safe?


A fault in your garage lighting might start a fire in the 8A wiring before the 16A fuse blows. Don't replace your fluorescent tubes with a huge bank of film-studio incandescent lighting.

I see nothing else to suggest it is unsafe.


  How much amps can I pull from each power point


From any one power point, you can pull the maximum current  that point is rated for (e.g. on a UK ring circuit I can pull 13A from any single power point)

However the total load on the circuit is determined by the circuit breaker rating for the circuit. It is perfectly normal to have ten 13A power points on a 32A circuit. Obviously you can't boil ten kettles at once.

You might have radial circuits (I'm not sure what is normal in Oz) and different numbers - but the same principles apply.


  Does it means I'm pulling 160 Amps from a 80 Amps main switch?


No, it means that the design used in all household electrical installations assumes that you wont fit every light socket with the most powerful bulb you can buy, plug a full kettle into every power point and turn them all on while simultaneously having a power-shower, roasting a turkey, frying four pancakes, mowing the lawn, drilling and sawing 2x4s, running AC at full, with TV, DVD, Blu-Ray, VHS, HiFi, bedside radio, and all lights on full blast. It might seem like your suburban neighbours do this but they don't really.


  On the garage "panel" ...


I would try switching them to see what happens. Inspect them first, maybe the fuse wire used doesn't match the number on the outside.


  90 extra amps


You say your main panel has a main switch rated for 80 Amps. It sounds like you need a 200A supply.

I'd 


Buy a power meter - the sort that clamps around your main power cable and tells you how many amps you are pulling. My electric co gave me one free.
Get whoever's installing the AC to specify total current that is needed at 
any one time.
Contact your electricity supply company / utility to get supply to house uprated accordingly.
Hire an electrician to replace your existing main panel with a new main panel with capacity for another 8 circuits (if that is really what is needed).
Get an extra job to pay for the electricity bills.