With angora rabbits, you do not kill the rabbit to harvest the wool, so no worries there.
Shearing is one option, plucking or combing the wool is another option.
Wikipedia tells the basics:
https://en.wikipedia.org/wiki/Angora_rabbit
It depends on how big and thick you want the blanket to be, and how much fur is produced by each rabbit.
It also depends on how long you want to spend collecting the wool. If you want to harvest enough wool on one day to make an entire blanket, it will take a large number of rabbits. But you could have only a few rabbits, and harvest their wool every few months, and eventually have enough for the blanket.
It also takes time to spin the wool into yarn, and make the yarn into a blanket. So you could be spinning some of the wool while the rabbits are growing more wool.
If you don't yet know how to spin, I would probably start by buying some angora rabbit wool and learning to spin. Or getting just one rabbit or a few rabbits, and learn to spin once you harvest the first amount of wool. As you get better at spinning and at caring for the rabbits, it will be easier to tell how many rabbits is the right number for you.
If you only want to make one throw blanket, it is probably cheaper and faster to buy angora wool for the project, rather than buying rabbits, rabbit cages, rabbit food, and so forth. So I suggest you only get angora rabbits if you want to spend time caring for the rabbits, or if you expect to keep spinning yarn and making projects as an ongoing thing.
I have not personally done it, but I would recommend whichever of the angora breeds is being raised by someone who lives in your area. Visiting in person, and talking to the person who is currently raising them, is a great source of information. That would be more valuable than trying to find a "better" breed that needs to be shipped a long distance to reach you.
