Wow. I recognize so much in that post. I think we probably all do. And I do think there's an answer.
Re: smoking and other bad habits. Which of us doesn't have bad habits we struggle to break? It's the human condition to live in the moment and to do things momentarily-pleasing that we know are not good for us in the long run.
It helps if we keep in mind all negative urges are the whispering of Satan in our ear as he seeks to claim what is not his. And Scripture tells us while God knows our susceptibility and our weakness and our unhealthy desires, He will always provide a defense against them...
"There hath no temptation taken you but such as is common to man: but God is faithful, who will not suffer you to be tempted above that ye are able; but will with the temptation also make a way to escape, that ye may be able to bear it." -- 1 Corinthians 10:13
And so we are told to rely on Him for the way out (which could well be, as you say, one of the reasons for them in the first place.) For the past few years I've found I am simply not successful at any undertaking unless and until I acknowledge His hand in my thinking and doing. When I push myself (and that's what it takes most of the time) to rely on Him alone, things change for the better.
Re: writing. Sports writer Red Smith said "writing is easy; you just sit down in front of the typewriter and open a vein." LOL.
But if writing is something you love and feel compelled to do and something that ultimately will glorify God by the words you choose to put down on paper, then pursue it. And be confident that He who began a good work in you will see it to conclusion.
Regarding procrastination, writers have that habit down to a fine art. No one can procrastinate like a writer. Norman Mailer said he procrastinated because only when he neared his deadline could he feel that surge of adrenaline that comes with being under the gun, and thus those negative voices in his (and every writer's) head were stilled by the need to write quickly.
It's a lot better, though, to benefit by Mailer's understanding and silence those negative voices before they begin without resorting to procrastination. How do we do that? By concentrating on the positive. We just go forth. Just do it.
Writing is like dieting. We say we need to be motivated before we can write. But that's backwards. If we write first without waiting for the motivation, that act itself becomes a motivating force and carries us to write more. Writers write, so just do it. Like most everything else, writing is a rhythm you have to get into. Once there, the rhythm itself carries you along. And that rhythm is God's hand supporting you and telling you He wants you happy and healthy as a true reflection of His glory on earth. That's God's will.
It seems perfectly rational and ordinarily normal to me that only in hindsight, a thing having been accomplished or not, can we say with any certainty, "This was indeed the Will of God."
Yes, that's 100% true. And it takes some effort to realize that what is true in hindsight has always been true, even from the foundation of the world.
The Lord cured me of two very bad habits which were in essence spiritual diseases. I had the sicknesses because they came before God in my life. They were my idols. You need to have a serious talk with yourself and ask yourself which do I want more, my smoking etc. or Jesus? He can end the addiction right away. I am living proof.
As for writing, you need to write every day even if you don't want to. Pick a time when you can do it, and treat it like going to work. Don't have any distractions. Try to do a set number of pages a day, every day, and you'll be surprised how easily it goes.