Like Jeff said the 4* is a great second plane, especially if you plan to get into pattern. Im also looking to get that Mustang and have been looking at it for some time, resist any urges to get it. That can possibly your 3 or 4 but not a second.
The 4* is actually one of the least expensive kits that sig makes.
I dont know anything about Ausy money but if its the same as my neighbours to the south (US) you should be fine. If you can get the kit its alot cheaper and not very difficult to build but requires just a couple tools. (#11 blade, razor saw, sand paper, etc..) This is a great flying plane (so im told, i haven't flown it yet).

Good luck,

Papa