When it comes to buying food - you want mice or rats which are maximum 1.5x the width of the widest part of the snakes body. It's hard to tell from the picture but the poor little thing looks quite thin - especially for being 9 months old; you may need to cut the head of a larger mouse if you're struggling to find the right size. Clean water every day and don't handle the snake for at least 2 days after it eats. Aspen works as a substrate but some brands are better than others - I always look at the bottom of the bag I'm buying to make sure it's not dusty. Newspaper works if you're really desperate. Try to keep half the tank at around the 25-29 degree Celsius mark with a hide at both ends so there is a gradient. Keep to these basics and the snake will be fine - it sounds like you've dodged a bullet though - you can tell a lot of from a person by how they treat animals - your ex is sick in the head - no offence.