Like others have said, I think this is a highly personal choice, but that you want to do your training with the same gear as you'll have on race day.
This year will be my 13th and 14th times on the mountain. Each year I reduce my gear more and more.
This year will be simply normal running shorts and shoes. A light shirt that I'll likely ditch 1/3 of the way in, if it's as hot as the last 2 years.
On most years, I find the weather/sun borderline too hot. I've permanently given up on wearing a hat. I feel 20° warmer in this race than a low elevation run.
(That said, pack your suitcase with extra gear in the event of a blizzard; you'll know the morning of the race what to wear).
I carry a hand held water bottle simply to sip more frequently, but you could easily make it between aid stations with nothing.
I've run in road and trail shoes with no real difference. Traction is rarely an issue, at least for a middle packer like me.
More important on the Marathon is something that fits well and won't impact your toes on the steep descent.
My personal favorite shoe is the Saucony Peregrine; low to the ground, good traction, snug fit, but room for toes to spread out and in case swelling is an issue.
Again, though, highly personal preference, and I think the correct answer is different for everyone. I saw several people with no shoes last year.