It totally depends on your height. I would aim your arm down and bend your elbows up so your arm makes a 90 degree angle and that's a good height to use the keyboard without lifting your arm up. Standing doesn't burn a ton of calories but its better on your body and helps you so you can stand longer. After you do it for a few weeks it's really easy. Make sure you have a cushion for your feet otherwise your back will hurt. I used a piece of 4" seat foam but you can but mats at the store.
I used a stand up desk for about a year then switched to a treadmill desk. Instead of buying one for $3,000 or whatever I took one of
These and took the top off and cut the metal so it was flat and put a granite counter top on it. I walk 6-8 miles a day if I'm working a lot from home at 2MPH.