Does this sound safe for a cat to live in?

I am hoping to get a cat this summer. I plan to adopt and give a deserving cat a good home, but I want to make sure before I adopt one that it will be completely safe and will have everything it needs. My mother doesn't want a cat indoors but she's completely fine with it being outdoors. In order to make it safe and comfortable I plan on building a large (20 ft x 20 ft) enclosure. It will be shielded from the elements and the cat will have a cat door to get in an out at it's own will and a larger door for me. I will put one of those play things in it, a scratching post, toys, food and water, blankets, a bed, and a litter box. I live on a four acre property and often wild animals like deer, rabbits and turkeys will venture in. We have chickens and every once in a while one will be taken by a hawk. Should this concern the safety of my future cat? I have researched heavily but in the end only another cat owners thoughts will be able to convince me if this will be safe or not. Also please tell me if anything sounds amiss in its living space or if I am missing something. Thank you.