The last few large orders we did (55+) took us-in actuality- 4 days to build. We generally ask our clients to give us the standard wait, 14 days, but then to give us a few extra "just in case". In case what? In case there were lengths that came in damaged, wrong, or just plain "off". Plus, we have other client pieces that were brought in before them, and we need to respect those customers.
Give yourself time to get the materials in and check them. Figure out how long its going to take you to cut the glass, foamboard, etc. I usually time myself with 1 piece, and figure from there. Your time is valuable.
At 50+ pieces, we give a 25% discount, at 100, we tend to go as high as 40%. I figure out retail and cost on these jobs, to see where the money is going, and how I can still make a decent profit. Find out what kind of deal your rep can get you; a lot of reps will give you an extra discount if you place an order like this with them.