To get into double degree programs you would have to satisfy the requirements of the single degrees. So if you wanted to do Law/Creative Arts I'm pretty sure you still have the UAI to get into straight law (i.e. 90+) as well as doing well in the interview/have a good portfolio to get into the...
If you're even considering doing extension Japanese you are probably quite apt at Continuers so you shouldn't drop that. But in saying that you seem to be just as good at physics. So I would advise you to keep both until you can decide (you might even change your mind and drop one of your other...
Maths subjects tend to make the maths/stats in economics quite simple. Although within economics degree I think they teach you all the maths/stats you need to survive (well, at least get through the subjects) although it doesn't go quite as in depth.
not doing maths doesn't stop you getting into any business degrees. if you're worried about maths though (they do have introductory maths/stats as part of any business courses) you can always do bridging courses
in manilla there's not much to do but go to the mall and visit relatives if you have any there. everywhere else is shit. go to the islands, visit boracay
there is no reason you can't get a high uai if not doing maths is your only worry. i know at least two with 99+ uai with no maths so you wont be disadvantaged there. not doing maths can limit your choices for uni though, but you're probably not going into a maths related field? (maths, science...
There are heaps of cadetships on offer in Wollongong, just keep a look out in the papers. I know of people who got cadetships at the end of first session. Also, if you get good marks and have heaps of experience it won't matter what uni you go to.