I'm always reluctant to critique but you did ask.
I'm not sure if the colours and tones are correct in those photos but thats all we have before us in this court, so lets assume they are.
It looks like a brown toned shirt, earthy not red toned, and broad bold checks.
Basically thats a casual shirt of some sort and in my mind as such doesn't work with a tie (unless a very casual /country wool knit) or a cut away collar.
In addition that kind of check doesn't do you, or anyone much, many favours. You'd be better to stick with a plain solid or stripes. If wearing large checks, unless at Pitti , its wise to break up the broadness with a jacket or cardigan or similar. So that theres not so much expanse of blocky squares and, graph paper like, bolded checks.
I know its against current trends, and perhaps, counter intuitive but in my eye you'd look better with a bit less fitting shirt around chest and particular stomach and waist.
Yes the sleeves could be a bit narrower at the upper ends.
The cuffs ( the actual cuff length not sleeve length) are too long and you would benefit from "normal" cuffs.
A bit of bloom or extra material in waist etc would allow the shirt to drape or hang and improve your overall look or silhouette.
The pants do look too low slung to me too.
I think your shape in particular would benefit from at least an inch or two higher waist line. It will slim you and make you legs look longer and improve the look of the shirt..
Think: fitting on top- loose below or fitting below - loose on top. You'll get a better over all look.
Belt or no belt is a personal preference but my "rule " if its a rule at all, is belt with any non -suit and no belt no loops only with suit.
No worries FXH I welcome all comments.
WRT the fabric, I think it's the palette of the photo. This is the fabric:
Here's the shirt in some better light:
Think you'll agree that it's appropriate beyond Pitti! The pants are essentially a grey flannel.
Agree with the fit comments, I don't think the juxtaposition of such a slim shirt with broad trousers works. It makes my legs and butt looks bigger than they actually are. The tweaks you mentioned are just what I was thinking of doing. 21" chest and 20" waist, combined with losing 1 or 2 kgs, would work wonders I think.
The cuff is long because it's a three button cuff. Just wanted to try something different with that shirt.
When you say "inch or higher waistline" are you referring to the shirt or pants?