Good question, partially answering and partially subbing to see what peeps say :)
In the summer I ALWAYS ride outside. Can't stand being in when it's warm.
In the winter, we ride outside when we can, and it's all dependent on the weather. In the last 2 months I think we've gone outside like 3 times.
That said, in my perfect world when it's nice when I want to be, I'd probably ride outside at least 3 times a week, and do schooling, gymnastics, poles, and groundwork inside. I don't really stick to a hard schedule, just do whatever we feel like that day, but keep it varied.
"There are two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle." -- Albert Einstein