size, especially for a snake that hasn't been taken care of adequately, could vary enough to make predicting difficult, but 1000g is probably a pretty fair guess for a year old snake.

This care sheet from this very website is pretty great: http://www.ball-pythons.net/modules/...warticle&id=59

I'd expect a BP at a year old to have moved on from mice to rats. A good way to judge size to feed is feed a rodent that is as thick as the snake's widest part. As dreese88 mentioned, another common method people use is feed 10-15% of the snake's weight.

When you pick this guy up, look for signs of being sick(respiratory infections in particular can be caused by improper husbandry), look for stuck shed, look for mites. Make sure to quarantine the BP from any other reptiles you have for a few months, I don't know how transferable BP infections can be to corn snakes but it's better to not take the risk.

If I think of anything else I'll let you know!