Many questions

Good job with brief questions.
Sorry about maximum verbosity on answer mode!

1 - Totally depends on you if sustainable. Some can and enjoy it.
All diets are counting calories in a sense. Either you mentally on paper (or app), or your body counts them by either losing, maintaining, or gaining weight.
People have gained fat weight on almost every diet possible (perhaps a few where you are fed and don't make choices as to quantity are exception).
If a diet has some automatic way of making you eat less than you burn, like throwing out almost all carbs, it'll work.
Sustainable is still on you though.

2 - it would be reasonable until you have 50 lbs left to lose. But you may not move enough and burn enough for 1000 calorie deficit to allow enough to eat for nutrition and safety. If a male consider 1500 minimum - therefore need to burn 2500 daily on average to allow that. If bed ridden, may not be possible. If a tad active, could be very possible.

3 - log first. calories matter more than what you eat. Log what you eat now to see where you are at. Then eat less.
You may want to cut out say 10 servings of sugar soda daily, which means little of the rest of your diet needs to be changed.
Then discover in yourself what foods cause you to blow it totally. Can't have a serving of chips without eating the whole bag? Well, is that smart to have around then.
Perhaps that's not an issue, and you have control, go for the 80/20 rule - 80% nutritious you enjoy and helps you adhere, 20% you enjoy and likely desserts (perhaps you really like brussels sprouts with butter - go for it).

4 - Focus on Health benefits first, first big chunk of weight lost will help your health immensely, and probably won't be huge for extra skin. Take a diet break every 10 lbs lost, for 1 week, slow the loss down that way. Don't allow going over 2 lbs weekly. And you can stop the weight loss at any point and hold that weight for a month even if you think skin getting too bad, because frankly it easily could be a problem, no way around it - if you lose too fast.

5 - Nothing magically changes the formula of eating less than you burn causes fat loss.
Many things can change what you feel like doing and therefore burning less (like thyroid issues). That can make it harder.
Many things can make self-control easier or harder, or motivation, or how your body handles stress and recovery and nutrition.
This is going to be an individual thing too.

You probably see a lot of self-experimentation in there - time to get the notebook out and make your health and weight loss a project. Not a study - studies end - this won't.
Not joking - make notes of discoveries - you'll have many. What works, what doesn't. And some of those could change even as body changes and attitude changes.

1) Is low carb like Atkins sustainable long term? Is counting calories more realistic? Calories matter for real weight loss... going low carb can result in loss of water weight even if you are not in a caloric deficit. Is your goal to lose weight or to simply see a slightly lower # on the scale? Whether eating low carb is sustainable long term depends on your preferences, and what you consider 'low carb'. But eating low carb while eating at a caloric deficit will result in weight loss. Just as eating moderate carb while also eating at a caloric deficit will lead to weight loss.
If you feel energetic, satiated eating lower carb: go for it, but remember calories matter.

2) I have about 150 plus pounds to lose. Should I start at 2 lbs a week, or less? With 150 to lose, you probably can aim for 2 pounds per week to start out. But it really is up to you. I would say to keep in mind this is a long term process and not a quick fix. When you set your profile for 2 pounds per week, what calorie goal are you given? Is this something that seems doable for you, for the next couple of years? If not, then try 1.5 pounds which would bump your calories up by 250 daily.

3) how do you get going and build momentum when it seems so hard to change habits from eating anything to counting everything? Progress rather than perfection. Pick one or two things to focus on NOW perhaps and add to it as you go. Logging everything you eat, as accurately & honestly as possible, is a good place to start.