I think the last statistics were that one in every two family law matters in Australia had at least one party representing themselves, so I would say it is fairly common. Of course, it’s always better to have a lawyer, but the cost of legal representation makes it unattainable to many, so they’re left with the choice of put up and shut up or represent yourself.
How risky it is to your case though really depends on your confidence and willingness to learn a bit about family law. The biggest challenge SRLs bring to the Court is not really knowing protocol and presenting documents that are half-baked - they’re unclear or missing information or distracted by issues not relevant to the matter at hand. But if you sit in on a few cases one day to see how things are done and use the many resources available to prepare yourself properly, it really isn’t as risky as it maybe sounds.
For your situation, I, personally, wouldn’t have any hesitation about representing myself because provided neither of you are a flight risk, equal freedom to take the child overseas for holidays is a no-brainer.