Planning a winter fish at Coro, Kings and Big reds being the target. Any tips or advice would be much appreciated as we are fairly new to this!

No, nothing at all ............must be a secret society up there 

Land based or boat?

Wai-Knot, lots of questions about your request.
And your starting comment, "at Coro" draws a blank for most folk.

1) Are you going to be in the Coromandel or going to be at Coromandel?
Big difference as to which coast you will be on and which waters you will be fishing.
Also which chart you will need to do some identification of fishing spots etc.
2) What sort of boat? A 6.5 metre with 100 hp will mean you can go almost anywhere but a 12 foot frying pan with 10 hp does restrict the fishing area.
3) Once you know where you are heading buy a paper chart of that area. Then sit down in your warm house and study it, which is much better than trying to use the chart plotter under canvas on the boat in the backyard in the middle of winter!
If you are going to Coromandel town, there are two charts to look at NZ5327 Waiheke to Coromandel and NZ5328 Coromandel Harbour. Both are valid depening onthe type of boat you are using.
Reading the charts you will see every Kingi structure, likely old man snapper habitat and the full picture of tides etc.
4) Study some fisho guides. Spot X or others. They give some good local information.

I admit I am useless on identifying the best boat ramps because I drive a 30 foot launch that has no trailer. But I am happy crusing the coast of Coromandel Peninsula from Squadron Bay to Boat Harbour.
And I admit it is a fantastic fishing and diving area. One of the best.

I might be tough on the need to study, but I had to do it as have many other fishos.
And many will admit they say finding that secret fishing spot took a lot of hard yakka.