I'm concerned about the 4m height of the wind gauge. Is that from ground height? The ideal position would be: As high as you can (not above 10 metres) in a position that has the lowest degree of elevation to anything that would abstuct wind.
So being far from tree's is great, but you need to get into the field of air that is free flowing and not effected by turbulance. I went from 5 metres and changed to 7 metres with cleaner air and my wind run increased by 50% on average. So placement will not only effect wind run (the amount of wind that passes by - calculated at every update and tallied to the end of the day, measured in km or miles), but also the gusts, wind speed and then any other calculation that require this info like Apparent temperature and Fire Danger Indexes.
With whatever height you go with, there is also info in the Wiki for Calibration multipliers to use depending on the height you go with, because as you go under 10m, the less wind it picks up, and thus the more calibration required to rectify the descrepancy.
As for the length, go the whole hog straight up! Don't dilly dally. Do what you got to do, if it don't work just go shorter. It's easier than trying to make it longer, particularly if you need to go somewhere for the cable to be made.
If it's a job worth doing (it is), then it's worth doing right.
I know it's just a hobby (like it is to nearly all of us), but it's always nice to know that it's giving credible data. In saying this, make sure your temp sensor isn't getting direct sunlight (add an extra shield or screen) BUT will pick up cool night air (not under a varandah like mine

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