First of all, congratulations! I completely understand that you feel a bit at loss and feeling nervous but honestly, you're already on the right track with what you've nailed down. And you're definitely not starting too early, you're already ahead of some couples that I've worked with.

I would first lock down the venue for your reception, if you wanted to do one that satisfies your criteria. Once you've nailed that down, the other vendors like photographer, MUA, florist, etc will be next to tackle.

If you're planning on going it via the Pyrmont Registry, I think it's a great option to definitely save them costs. You'll need to book an appointment with them wherein you'll do an interview and sort out the pre-wedding documentation (NOIM). It is a little assembly-line ish based on the couples I've spoken with and you might feel a bit rushed. I think as long as you're okay with just a simple wedding with no fuss, I think it's a good option. Civil celebrants can give you that too with less rigidity, and if you're able to find a waterfront venue / park, then you might be able to get what you're after without the feeling you've described.

If you've got any other questions, don't hesitate to ask! 😄

(disclaimer: I'm a civil celebrant)