<human>: My cat, Toulouse, has been an indoor cat only since I picked him up from a farm as a kitty. He has spent most of his life living with other pets. That sufficiently provided enough stimulation and exercise for him. He has now been living as a single pet with me for the 9 months. Toulouse has started developing some behavioral issues in the last couple of months that have only gotten worse. He's put on weight, cries constantly, but my biggest concern is that he has starting biting people. Nipping might be a more appropriate term. It seems territorial in nature, but I'm not sure. 

I know he doesn't get enough stimulation now. I live with two other people in a large apartment but he doesn't run around chasing dogs or cats like he used to. I try to play with him but I struggle to find toys that will interest him for more than a few minutes at a time. I've taken him on a couple of walks. He's done relatively well. He shows a lot of interest while we are outside and spends most of his life sitting in windows. 

I'm considering letting him spend some time outside by himself. I want him to live a healthy life and have a chance to be mentally and physically exercised. I'm afraid I'm not providing him the best environment currently. As far as his physical safety goes, he has a microchip. He's been spayed. I know he would need a collar and a tag as well. He has his claws. I know I would need to keep him on flea medication. Are there any other measures I would need to consider before letting him out? Speaking mentally, can a four-year-old cat transition into a part-time outdoor feline successfully? Are there things I can try with indoors to help him be happier with his current living situation? Any feedback would be greatly appreciated.

Can you condense the text into a few key points?
<bot>: Four-year-old indoor only cat is getting fat and mean. I am wondering if letting him outside periodically would help his overall well-being.