You can go to the National Weight Control Registry for a lot of good research, but what both they and Consumer Reports research found was that success was very individual- it is what works for you. He is trying to do something that is highly unlikely- less than 1% of the tiny amount of people who successfully lose 65 lbs or more keep it off for five years or more. So with that in mind, I think there is a sort of split advice-
First, don't get down on yourself. You did not cause this to happen. It isn't because you have bad self control, or bad habits or all the other crap that gets thrown out there. Your body is, for whatever reason, different and requires intensive management. As part of that, I would say set reasonable goals. If you can land at 350 and maintain, that's a huge win over 450. Half of excess weigh is how "success" is defined in weight loss research.
Second, if you are going to succeed you are doing something rare and heroic and extreme, which means going all in. This is going to take time and dedication and effort and it may mean scaling back other activities and hobbies.
People with a support system are far more likely to succeed. NC has an extensive OA network, some meetings better than others. Or Weight Watchers, which few here are going to like suggested, but the in person meetings and continued support about double the chances of success and they are extremely available. You can find leaders who have lost more than 100 pounds and if you go that direction I would seek them out since IMHO the newer WWer systems are better suited to people with less to lose and an experienced large loser can help navigate the differences. if in the triangle Rex Hospital has an obesity treatment team with a Primal physician that is supposed to be very good. Duke of course has the Rice Diet Center. Both of these provide long term support which is effective for some people.