Avocado question

Last summer just for fun I planted an avocado pit in the little garden bed in front of my dining room window. It was more of an experiment than anything. It actually grew a little baby tree. We had some frost this winter and it looked dead.

Apparently the roots were still healthy because it is back. In fact now it looks like two baby trees. So now I have some questions.

First how big do these things get? I need to know if I need to move it.

Second if I do need to move it when is the best time? Should I wait for a certain size?

Do I need two trees to get fruit when they are mature?

I am so utterly clueless 

What zone are you in? As far as the general info a quick google search can help you out. As for the fruiting part of it, most sources I have read say that its a crapshoot if you will actually get good fruit since commercial varieties don't come true from seed. You would need 2 trees a male and female in order to get fruit. Good Luck!