Hi kiwinoz62 and welcome to the ANZLF!
Humidity issues have caused a great deal of pain to builders for all of time but only when they disregarded RH and some of the great advice already posted in this thread and others.
But since you understand this in advance you will do fine I am sure.
As mentioned the temp considerations are more for builder comfort although temperature can impact how much or how little water the air will hold. It also can greatly impact how glues and finishes cure.
I live in the Midwestern United States, Michigan home of ground zero for the death of the US auto industry to be precise... Our winters can be sub-zero F for short periods of time and our summers can approach, although rarely, 100F. As such I have to dehumidify in the spring, summer, and early fall and humidify in the fall, winter, and early spring. On some days I have to do both in a single day but not at the same time.
So I am always either hauling water away from my dehumidifier or schlepping it to the humidifier. I feel like a water boy on a sports team...
But, regardless of the effort required my shop maintains a 42 - 48% RH and 72 - 77F temp at all times. It's a basement shop that I walled off and insulated with R-13. The house is built in sand which acts like a giant cat litter box wicking away moisture from the structure.
My dehumidifier is a 30ish pint Goldstar that seems to work fine and it's currently in it's 4th year of use. Dehumidifiers will give off a great deal of heat which is a bit of a problem in the summer since it warms up my shop to the level where I am killing various lights so that I can stand to work in the place. They are also noisy and in my opinion its the kind of grinding, relentless noise that wears on me...
I was going to plumb my dehumidifier with a hose to the sump pump but once I had my drywalled walls painted I just couldn't bring myself to punch a hole in my walls.
For several years I used a humidifier with a wick/filter and that worked fine except that the wicks need frequent cleaning (not a fun job...) and the performance of wick based humidifiers is greatly impacted by the condition of the wick. It would perform very well for a couple of days with a clean wick and then it would start to perform poorly until I cleaned or replaced the wick.
I just purchased an "Air-O-Swiss" humidifier and I am in the 24 hour soak/wait cycle right now setting it up to turn on later this evening. The furnace is now on here in Michigan which means that the dehumidifier gets shut off and the new humidifier gets set-up and turned on.
I bought this thing because it does not use wicks or filters and instead vibrates the water with ultra-high-frequency to atomize the water into a mist. In addition it has a demineralization cartridge that cleans the water going into the tank and an ionic silver stick that uses the power of silver to kill bacteria.
But wait - there's more...
This unit will also heat the water to 190ish F killing bacteria and then mist the humidity into the shop at 105F. It uses the same amount of power as a 40 watt light bulb.
I am very interested to see how this unit does and also very grateful to not have to be cleaning stinkin humidifier filters any more.... In addition, a couple of times a week I have players/friends over to jam in my shop and in the age of the swine flu I thought that an anti-bacterial humidifier might be a plus.
Anyway the point of all of my nonsense here is that it's standard fare for wooden instrument builders to have to go to some great lengths to have a properly set-up environment to build. And once you determine what will work best for you it's on to the great fun of building.
Welcome aboard.