Hello, Esther! Smart casual is to dresscodes what oxymoron is to literature; it's so easy to go overboard - either too casual or too smart/formal! That said, you needn't worry about it because you nailed it with your red, white black palette and the silk (silk-like) luxurious tops.
I am for team Beltless. But somehow I prefer the belted version of the red trouser outfit. Maybe I would let the tuck more relaxed, covering more of the belt... But I am not the biggest on proportion knowledge, so please take this advise with a grain of salt (and follow other YLFabbers' advice on this one)
Plus I would swap the beige bra for a strapless (you can also try one with black straps or animal print in black/white as per recent Angie post on how to deliberate show bra straps. I guess that would be a funky choice, but the strapless is sure much more appropriate to the smart casual setting.)
Regarding the sandals, go for the finer one.
PS: On short shorts... the endless discussion. Lantana has a point when suggesting you swap the short shorts for longer versions. A indoors smart casual setting might require a little more coverage. However, I love short shorts and if the weeding/wedding surround events aren't too traditional (are outdoors, the sun is scorching on the South during the wedding period), I would keep them. (I <3 Hart of Dixie's style; Rachel Bison is 31 and still rocks shorts!)