Hi John
The advice about low tide is basically to ensure that you have clearance under the bridges. However if you moor at the yacht station this isn't an issue as its before the bridges. If you moor there around low tide, it runs quite fast, you would be better to go through the bridges, turn and come back against the tide. The only place to moor at GY is the yacht station, the old Marina Quays in not safe.
There are buses or the train. You could catch a bus or train from Acle although the village is quite a walk from the river.
PS agree with others, bus or train good idea - even a cab if your feeling a bit flush although it shouldn't be a fortune.