As someone who's tried every diet and training regiment under the sun, and never (before or after) being outside of "normal" BMI and of varying levels of athletic (maxing out at 10 push-ups through 30 dead-hang pullups):
On your first point, yes. Most diets work, as long as they fit with your persona and schedule. Anything you feel comfortable with and can stick to. Just by "doing" a diet, you end up being a lot more conscious of what you put in yourself.
When someone asks me for advice, it's mostly the same:
* Write down everything you eat for two weeks, weigh yourself before and after. The initial point was to measure your actual TDEE, but people invaribaly end up eating less and losing weight during those two weeks because they don't want to write down "half a package of Ritz crackers" in their log.
* Take an honest before pic. When you think you've stopped progressing after a few weeks after the initial burst, being able to compare backwards is invaluable as a motivator.
> When you eat less, the body adapts by working more energy efficient. So you eat 10% less, meaning the body can use only 90% of the normal energy supply. It react by using only 85%, storing that extra 5% in case things get worse later on. So the body expects that later on, supply could drop to 70% or much less. Then those stored 5% are really useful.
This is however not anything I'm comfortable believing before I read it from reputable sources. From a strict weight standpoint, I've rarely seen anything that doesn't align to your TDEE mainly differing by your weight and muscle/body ratio, unless chemically induced.
There was a recent study on alcohol in this scenario, but even that mostly indicated the effects on hunger, not on energy expenditure: https://www.ncbi.nlm.nih.gov/pubmedhealth/behindtheheadlines...
While I'd say that the keto diet works, it's not very practical, when accounting for eating in restaurants, socially (other people cooking for you, you cooking for others), etc.
What is your goal? Just losing weight? Being healthier? Body recomposition?
What is your life today? Could you cut out something you indulge in now? Alcohol, snacks, sugar in your drinks? Would you be content in cutting those out?
Do you work out? Could you see yourself doing that a few times a week? What would you enjoy doing? Hard 7 minute work-outs daily? Fun climbing/swimming/rowing/hiking? Lifting in gyms?
TLDR; Whatever diet/routine works is whatever you can stick with. I hate running/endurance training, so HIIT and calisthenics is what I've had most fun with. Would love climbing if I didn't hate heights :)