I think there is a vast conspiracy to make the world average - whether you’re my size (6’4", 225lbs - I’m not that fat!) or you’re shrimpy you’re out of luck.
I wear a suit 3-4 days a week to visit customers and my advice is this: if you can afford it, I would go custom tailored. It’s not that much more expensive than a top-end off-the-peg suit, but it will fit you so much better and look so much better, and if your tailor is any good, it will last a lot longer and therefore, even though being slightly more expensive, will be a better deal long-term. But even if you don’t go whole-hog and get a fully tailored suit, I would still get a tailor to give it a once-over and make sure it’s fitted to your husband’s frame, especially if he’s not ‘average’ in size / shape.
Don’t go trendy in the jacket - if you get one that’s conservative it will last years and years - 3-button single-breasted is pretty much the standard, with one side-pockets on either side and a breast pocket, and the lining should be a shiny lighter-coloured synthetic fabric. Simple, classic, and standard - wool is the best, and before you say ‘eww itchy’ it can be brushed quite smooth. You can have one or two splits in the back - either is fine, although a double-split (i.e. slit on either side of the bum) is more traditional and IMO wears better. Trousers should be flat-fronted although tall skinny guys can pull off pleats; make sure they are long enough to have a single break, just above the shoes, and try them on with the shoes he’s planning on wearing. Shirts - go for single-cuff, with both buttons and a cufflink hole (not sure what this is called) as IMO an average suit can be made more stylish with the simple addition of some nice cufflinks and most folks in the US don’t wear them so he will stand out a bit. Go for either a subtle pattern or solid colours in the shirt material, and go for 100% cotton with a tight weave, and don’t feel like you need to wear white only - IMO plain white should be avoided. Avoid button-down and big huge collars. Some shirts have two collar buttons which I like, but if he’s wearing a tie it’s a bit lost. And make sure the shirt fits properly - nothing looks worse than a shirt that is either too short in the sleeves or too tight in the neck - it looks like the poor schmuck is getting hanged!
A little colour in your shirt goes a long way. Make sure the tie is the opposite of the shirt - if he’s wearing a solid shirt, then a pattern tie, or if pattern shirt then solid tie. If you want to be super trendy get a tie and a shirt that match in colour and are both solid, with a matching handkerchief in the breast pocket - this can be quite a cool look. Solid metallic ties are quite trendy just now as well. Buy silk - artificial ties look like crap, and cotton ones look ancient. Silk is definitely the way to go. Socks should be dark coloured (unless you’re confident enough to pull off great stripey socks or something, in which case they should clash with everything else he’s wearing) and should be a mix of cotton and synthetics but don’t even think about wearing white socks no matter what. Shoes should be dark (black or brown), match his belt, be well polished (i.e. shiny, especially for a wedding), and if you MUST have a pattern on the shoes, then a brogue (aka wingtips) is about as far as I would go. For best all-round use get nice smooth toed shoes. I hate men’s shoes with buckles or any sort of mettalic crap on them, and you can’t pull off boat shoes unless you’re wearing a linen suit. Black suit means black shoes and belt; black suit + brown shoes & belt = awful.
As for specifically dressing for a wedding, it depends on the time of day. Wearing a black suit during the day is to be avoided, so for a daytime ceremony I would recommend dark grey or navy blue. He can also then re-use the suit later for other purposes; blue and dark grey are pretty bog-standard wherever you go so would work fine for this occasion. However, black suits (like tuxedos) are de rigeur for evening affairs, so it really depends on time of day. Even the best of black suits looks funeral, however, so if he wants to wear it for other funtions then a colourful shirt / tie combo is advised.
Not sure if you get them in your area, but a store out on the West Coast called Men’s Wearhouse is very good IMO - lots of selection, and lots of variety in sizes, and staff that actually seem to know what they’re talking about 