I might go with a tie that brings a little color into the mixture, just for contrast with the light grey suit and pale blue shirt. Yeah, a black and silver Maccesfield is more of a traditional wedding tie, but with that suit, it probably wouldn't be my choice. (Hey, it's okay to violate a traditional rule, so long as you do it knowingly, and for a valid reason.)
But you know what? It occurs to me that if you were to stick with the yellow shirt, with that suit, a solid black grenadine (or knit) tie might just look okay. It's not a shirt/tie combination I'd wear to a wedding, but I'm just saying, light grey suit, yellow shirt, and black tie, might not be all that bad a choice.
I'd also probably wear black shoes with that suit, before walnut shoes. (The people who insist that black shoes are never a good choice, are as foolish as the ones who insist that black shoes are always a good choice.)
Socks? Is this really a tough one? Heck, wear charcoal socks, or socks the color of your colorful tie, or red-blue-and-yellow argyles, or any of a hundred other choices.
Since you also asked about the pocket square... the one pictured isn't horrible, I guess, but it'd be easy to do better. Picking a pocket square isn't all that difficult. Find one in an appropriate texture, which ties in with a minor color in some other item of clothing (most often, a necktie) you're wearing, and it'll probably work. Otherwise, wear a white linen square with a colored border. Or something else, if you like. Choosing a pocket square isn't something for which extended analysis is really appropriate. Choose it mainly on instinct. If you don't have sufficient confidence in your instincts, fine, then just go with plain white, or don't wear a pocket square at all. (Similarly, people who spend inordinate amounts of time carefully folding, measuring, and positioning a pocket square, are just over-thinking the whole thing.)
Of course, what I'm describing is nothing at all like the look you indicated you wanted to pull off. Primarily because I think that look is terrible.