I think you're close Rider. I'm going through the same process but Mrs H is also my accountant so I don't get too involved personally.
The important thing is that you can't issue a "Tax Invoice", and while you are free to make any mark-up you think the market will bear, you cannot say 10% of it is GST. Remember the client cannot claim back any GST so may go with another supplier who can issue a Tax Invoice.
Be careful also if you have recently spent up on capital equipment recently. You may be asked to repay some or all of GST returned to you. I'm OK my van is 10 years old.
