Re: What is the difference between 'It's Wed' and 'Wed it is'?
I find "OK, it's Wednesday" rather unnatural. If, as in your example, you have been discussing which day to meet and you eventually settle on Wednesday, then we would say "OK, Wednesday it is".
Note that we never say "Wed" as a contraction of Wednesday. You'll see it in writing, but in spoken English we always use the full word, so your post should have had the full word in each quote.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.