Wanting to buy a dirt bike

So my family bought a good amount of land in the middle of the country and I immediately wanted to get a dirt bike. However, I don't know much about dirt bikes... So I am asking if anyone has any advice about buying a dirt bike.

I want to get a decent used one for cheap. My budget is about $1000. I have been looking on Craigslist every week or so, but I don't really know exactly what I'm looking for. I'm an adult and I don't want one of the kiddy ones, but I don't want one that would be too big. Also, I want to be able to go fast, but not deathly fast, so I was thinking about 150cc's, but not sure. And maybe only a 2 stroke engine to cut down on the maintenance.

What do you guys think, can you offer me any advice about buying my first dirt bike? What to look for, what to expect, anything like that. Any help would be appreciated.