As far as if you think it's a large task, in my opinion, it's going to depend on:
1: Comfort / confidence level in yourself
2: Willingness to make mistakes (which may cost $$$)
3: Ability to set aside large blocks of time to devote yourself to it since you're learning as you go
4: Can you source parts
5: Is your investment in time worth it (ie if youre really busy you're better off paying a pro)
6: Do you want a challenge
I personally like taking (calculated) risks, but I'm also learning and sometimes pressed for time. Any time you learn something, it will usually take longer the first go. I've spent weeks on the top end of my engine to research, carefully dismantle and solicit help when I get stumped. For a lot of the guys here, what I'm doing may take a day or a weekend.
If you can invest the time to learn, you can do it. Just make sure you find good resources (plenty of them here).
As far as dismantling and sending to a expert... well... it depends. Many shops will reduce your bill if there's less labor involved. But, on the other hand they may not want to take a risk on working on something you're putting in. They can't guarantee it'll work, so they may not want to take the job. Lots of chain shops in the US are like this due to liability issues.
The A/C system itself is relatively simple, but you need to be cautious because you're dealing with a pressurized system.
You can train for MVAC/HVAC certification in the USA relatively easy. Take a test on laws and proper procedures and you're set. This isn't necesary, but I did do it since it only cost about $35 IIRC. Sorry, forgot you're in Oz--your laws are quite a bit different in some instances
There is a difference between knowing the ideas (ie what the textbooks / manuals say) and what will happen wen you're actually doing the procedure. I find there's always a thing or two you don't learn in the book that you find only through experience. That's partly why we have experts... they've been there, done that and know the quirks and ins and outs.
I think you should carefully consider whether you think you should undertake this job yourself. Read up what others have done and their experiences. You'll likely need tools and equipment you don't have right now.
When it comes down to it, it's all up to you. Just be careful and thoughtful in your approach and don't bite off more than you can chew ... it may cost you more in the end.
Sorry for the longwinded reply, but that's just my take on it.