I would never wear black trousers with a navy blazer, even in brilliant sunlight. In the dark you'd look like you are wearing a strange fitting suit. Stick with grey, khaki, cream and white, maybe even a very pale blue.
If it was me, I'd go for off white or pale cream trousers with plain black shoes not brogues. I'd go with a pale blue solid pattern shirt or a black and white gingham pattern, both with button collars. I wouldn't wear a neck tie unless it's a DB blazer and I'd probably go with a loosely folded pocket square in a blue, navy and gold pattern.
When I've asked for trousers to be taken-in the tailors alsways wants to do it from the knee downwards but sometimes I have to tell him I want some of the slack taken out of the thigh area too. I too have large calf muscles which tends to cause problems with legs riding up and sticking or holding a crease. Therefore for dress trousers I tend to ge for bottoms around 17 or 17.5 inches.
For me, I hate bunching at the bottom of the leg so the width of the trouser bottom...
It's all personal opinion so go with what you feel. I can't really tell what colour the suit is but if it's black or charcoal I'd go for black shoes. If you want to wear that shirt, maybe a dark blue tie with a small white pattern. I quite like the idea of burgundy shoes though, maybe with a purple tie and preferably a white shirt with a purple/pinkish pattern. Sometimes you just have to spend ages just testing stuff out.
Personally I wouldn't look at the blazer in isolation, I'd look at what you are going to pair it with and the overall cut of the garment. I once wore a navy blazer with white buttons to match the white chinos I wore, maybe with a pale blue shirt and desert boots or oxblood shoes and I'd often stuff a blue pocket square with white polka dots in the pocket. I realise this might not be everyone's cup of tea but it suited me.
Half-way house, I can't really tell from the picture. I have some chisels around one Inch and some around two inch. Maybe square starts at three inch I don't know. Still, what does it matter just so long as you like them?
Trousers are too long IMO, I don't like any roll around the bottom when stood up. If you're going to wear short sleeves to show off your cuffs make sure the length of the jacket is short too, yours looks a little too long. Hvae it shortened by 2 inches.
I'd say, wear what you want. Personally, I don't do fashion, I do clothes. I don't want to be like the majority of other people - why fit in when you can stand out?
The only thing I would say is that there are around three choices when putting together an outfit:
Colour: Should Compliment
Cut of garment in relation to what other piece of clothing you are wearing. Try not to mix styles and periods of clothing.
Texture. Try to avoid mixing course...