Is 1640 calories too much for a man that weighs 302 pounds?

Anything over 1200 is safe for an adult. If you're able to get through your day with normal energy at that low a calorie count, the weight will come off faster.

But because you're pretty big now, with bigger calorie needs to maintain your present size, you don't have to routinely go that low. You'd still lose eating a lot more calories on a typical day.

BTW, good for you, making serious changes. Don't think of it as a diet to lose weight but a change to healthy eating for the rest of your life. Weight loss is just the bonus.

That is probably a good amount actually.

Use the calculator here to help you determine what your daily intake should be, based on your current stats and activity level https://www.freedieting.com/calorie-calculator

Cut out 400 calories, carbs and sugars (even natural sugars).

It isn't too much.  It might be too few.  What's more important is the nutrients you're getting in that 1640 calories.  When you are in a significant calorie deficit trying to lose fat, it is very important that you have plenty of protein, vitamins, minerals, and essential fatty acids.  You want to watch out for foods that are high in carbs and sugar but have low nutrient value.  

If you can maintain your normal activity level and don't feel hungry, 1600 is fine.  If you are starving, light-headed, or lack energy, consider increasing your intake of high-nutrient foods and the resulting calories.