After sports injury, I gained a lot weight. How to lose my weight?

Hello doctor,

I am a 24-year-old male who has spent the last three years severely overweight. I had a sports injury and I packed on a lot of weight afterward. In total around 100 pounds. I felt fairly healthy at 6'1 280 pounds I was playing collegiate rugby.

I decided to make a change in the last two weeks and I have completely cut out sweets, candy, soda, fast food, and junk for the most part. I have been eating once a day, midday a meal that consists of rice, fish, chicken, salad, and sweet potatoes. It would be around 800-1000 calories. I take around a 30 minutes walk that I have been building upon with light bodyweight exercise. Just going as I feel comfortable.

So my question is do you think going from a 3000-4000 calorie a day diet and dropping to 1000 a day is too drastic? I am trying to cut a lot of weight I am hoping around 75 pounds in the next three months. I feel fine and it is not overly fatiguing. I take multivitamins and if I feel really hungry or have a sweet tooth I just have a spoon or two of peanut butter. When I started I was 388 pounds and today I weighed myself at 373. My water intake has been consistent as well.

Just wondering if what I am trying to accomplish is attainable or realistic and if it is fine for my long term health. I feel like obesity is just as bad. Looking forward to your response.