A3's better to start with, but don't try and make it full size so if you go over you've got room to expand into.
When I draw maps I pencil in the rough layout of the main thoroughfares, any wide open spaces such as market squares, large important buildings then fill in smaller buildings before inking. If you want I can try and dig up some maps of mine to illustrate what I mean.
I guess an important question is how detailed and in what style you want the map as well, as that will dictate the best way to create it.
As a side note if you want to make a more realistic feeling city, it is best to not try and have everything in neat little blocks as it is an inorganic way for a city to grow. By that I mean how did all the temples end up together? The city likely will have grown from the river backwards so there would perhaps be lesser temples closer to the waterfront, with the larger ones built later when the city had more money.
There would probably be several marketplaces throughout the city, especially a large trading port.
Similarly the castle would be positioned on the best ground for defence when it was built, which could possibly place it on the outskirts of the city, or quite close to the centre.
But I could just be overthinking it all