Desperately Seeking Advice

Citizens, I need some help.

I should be finished with the Mermaid Mesh sleeve this afternoon. Since this is my first attempt at a lace garment, I have a question about blocking/seaming. Should I wash the pieces, block then sew together, or dampen, block then sew together or sew together, wash then block? The 100% cotton yarn that I'm using needs to open up a bit...since I'm looking at 3/4 sleeves in stead of long ones in it's current state.

Any help you can give is always appreciated!