1. Absolutely. Visualization skills give you a huge advantage in architecture school. It's easy to fall into the trap of letting handsome images mask underdeveloped projects, though, so you should be careful not to lean on those skills too hard. But most students are learning visualization as they go, so you'll be able to spend that much more time refining your design work. 

2. You should finish your bachelor's and then pursue an M.Arch. Your art background will likely make your application portfolio a cakewalk, and more importantly, you don't want to be in architecture school with 18-year-olds if you can help it. The "solid foundation" thing is not really how it works, and you'll get more out of your interactions with adult peers to outweigh any benefits of the B.Arch. 

3. Technically (for licensure), a B.Arch and an M.Arch are equivalent degrees. The portfolio is what matters. In my experience M.Arch portfolios tend to be substantially less obnoxious, and M.Arch holders have more varied life experience, so if anything I'd give the edge to the M.Arch. 

4. I haven't the foggiest idea. 

Have you read more into the current state of the field, or do you just 'dream' to be an architect?

I would suggest reading more about the field before just wanting to be an architect. It's a battlefield out there... including Australia. This is a very saturated market wherever you go. Tons of high qualified individuals competing for a very small amount of jobs... and alot of lack luster jobs at that. That means you don't get to do very interesting things...think fire separation studies, egress studies, and accessibility studies. This is very very boring work.     

There is definitely money in rendering buildings and architectural scenes, but usually it is done outta house. Starchitect's offices may have an in house person to do it, but starchitects don't pay much at all, if anything since you are working for a sweet resume.

I'm sure there will be ppl that say this is a pessimistic outlook, but I was in architecture for 8 years (aacredited & mater degree) before realizing that you're basically crazy if you think you can over come the hoards of very qualified individuals that also 'dream' of being an architect. It is pure economics... low demand & huge surplus of smart architects and the like.

I make way more being a traveling artist than I ever did in the architectural industry. Life isn't perfect, but at least I have money packed away for the bad times, and won't be on the curb when the next bubble pops.

@loulouish

You're going to get a lot of the cynical and jaded feedback in the previous post. And not without good reason; a ton of folks got seriously screwed when the bottom fell out of the economy a few years ago. 

You should think about what you hope to get out of the profession (the money-to-work ratio isn't great, relatively speaking, so if money is a motivator, you're barking up the wroooong tree), and as many architecture professors have said, "if you can imagine yourself doing anything other than architecture, then architecture is probably not for you."

That said, if it's what you want to do, don't resist that because other people have had a hard time. It's getting a lot better (I'm in my last year of school and I have three offers waiting for after I graduate; that's not typical, but 3-4 years ago it wasn't possible).