5 feet for the Weather station over grass area. You will be fine. Think of it this way, unless you are a squirrel or bird, you live on the ground . Keep the ISS 5 feet and you can maintain it. you will need to periodically clean out the rain bucket, change battery in the ISS and stuff.
I have, on my setup, a similar setup you are talking about. i used a tripod, with the feet held into the ground with 3 foot threaded rods with a nut on the top. It hasn't moved since I put it in in 1993. The anemometer is 30 feet off the ground and has been faithfully behaving since 1993 which is a heck of a long time. Just recently it has stopped moving, I have a pole to tap it with and it moves it, it works for a while and quits. I have theories on that one. What I do know is I can't bring it down to replace it. It is up there. 20 years ago No problem. I would lift the pole out of the tripod, replace things and put it back, but now time has worn me down. So it is up there. I did add a lower anemometer about 10 feet and it works fine.
I suggest in retrospect on your pole, get a telescoping flag pole, something you can lower as you get older to service that unit. If you get the same length of time on your unit as I did on mine, you will be a happy camper.
the wife will learn to be happy and enjoy it. I put a console in the kitchen, the wife checks it daily and often tells me what I already know.
Here is my URL on my setup
http://www.desmoinesweather.org/weatherlink/main-station.html if you have questions, ask away