There are countless personal factors, such as your genetics, current fitness level, past exercise and daily habits, that will determine your total daily energy expenditure (TDEE). The calculators don't, and can't, take all of those into account. They can provide a decent ballpark figure, but that's about it. So instead, I suggest you simply take the empirical approach to find actual hard data that applies to you.
Since you say you are not in a rush (very wise) I suggest the following. For the following three weeks, track EVERYTHING you eat in an application such as MyFitnessPal. Eat as you usually would. Don't let the sudden awareness of your consumption habits suddenly change them. There's a first pitfall here: you must be extremely critical of all entries you find on MyFitnessPal because, my word, many of them are wrong. When consuming food with labels, cross-check any entry you haven't made yourself with the label and correct if necessary. When consuming whole foods, I like to cross-check with the Nutritiondata database, which is an excellent resource. Weigh your food using a kitchen scale (preferably an accurate, electronic one), don't just eyeball it. Use weight measurements instead of things like "cups" or "portions" because they can vary too easily. While doing all of this, weigh yourself daily and record the weight in a spreadsheet (such as on Google Drive). Preferably use an electronic scale that provides accurate information with a small resolution (down to 0.1 kg or lbs would suffice). Weigh yourself in the morning, immediately after going to the toilet but before eating or drinking something. This will give the most consistent results. There will be perfectly normal daily fluctuations in weight; ignore those. At the end of each week, take the average of the weigh-ins. That's your average weight for the week.
Now you can observe how your weight evolves over those three weeks. Does it increase? Then on average you are eating more than your TDEE. Does it decrease? You're in a caloric deficit. If it stays more or less the same, bingo, you're eating maintenance. Suppose you're 280.2 lbs the first week, 280.3 the second and back to 280.2 the third, it would be the latter case. Seeing a rising or sinking trend would indicate surplus/deficit. Find out how much you ate on average by averaging the daily calorie intake over those three weeks.
If there's weight gain, your TDEE is lower than what you currently eat. How much lower depends on the actual weight gain and absolute calorie consumption. It's the other way around for weight loss (you're eating less than TDEE). A good start for adjustment would be about 250 kcal for a male. If you're very patient, you might repeat the experiment above with an adjusted calorie intake and see whether the weight gain/loss stops (or reverses) to zone in further on the exact number.
Armed with this experimental knowledge of your TDEE, you can now decide on the calorie deficit you wish to create and stick to that by using the tracking you've become accustomed to. Let me give you a fair warning: too great a deficit cannot be maintained. Build habits that can be kept in the long run (as in, your entire life) and make the deficit a scaled-down version of what you'll be doing after you've lost sufficient weight and eating maintenance.
Good luck!
