No disrespect intended but if its your first time launching with a new boat, I would be thinking about avoiding the harbour, and trying to find somewhere quieter and a less busy time of day (i.e. not the weekend if you can at all avoid it). Tunks Park will be busy on Sunday if the weather forecast is to be believed - I would stick to somewhere like Pittwater/Hawkesbury/Berowra which might be a bit quieter. On a weekend the main harbour will most likely be choppy from all the wash if you go further than the spit - what sort of size boat have you got? Might be best to leave it until you are a bit more experienced?
Dont worry too much about the fishing for your first time out, maybe just throw in a rod and a few lures, you will probably be too busy figuring out the boat to focus on the fishing, but I wouldnt be surprised if you found a few salmon on the surface in Pittwater or one of the branches of the Hawkesbury, or maybe a few flatties.