Q1: Why did everyone wear mid 1900's clothing?
So far as I can tell, gold and silver lame fabric didn't exist at the time of the movie setting. So why did we see all the players surrounded by people in lame? My understanding of the time is that yes, Pharaoh and his house might have had a few hundred seamstresses hanging about, but where did the raw cloth come from. There was an awful lot of silk being flashed on screen at a time when there was no established silk trade with China. And for that matter, the historical records of the time point to rather poor dress in coarse cloth as the norm for every day wear.
My suspicion is that DeMille recognized that people wanted to see a spectacle, not a bunch of grubbily dressed actors and actresses. But couldn't he have been a bit saner in the costume choice?
Q2. Why did the parted Red Sea not have a wet seabed?
One can always cop out and claim God dried the sea bed as he parted the seas, but surely someone who wrote the gospels would have commented on that even greater miracle. After all, a lot of them commented on the parting of the sea which is minor compared to instant drying of the sea bed. I think DeMille just didn't want to gum up the costume works with all that mud.
Q3. Why did the charioteers not try to escape as the sea closed on them?
It would seem that most sane people would at least make a token effort to get to shore when the walls of sea water started to close around them. But all the extras in this movie just stood there. Maybe there was a lower price for extras who didn't move around?
Q4. Why did Pharaoh keep trying to twit Moses after repeatedly getting his nether regions handed to him every time?
Most rulers are smart enough to go with the flow when it is clear which way the wind is blowing, but not Pharaoh. Now here DeMille is no worse than the record as recorded in the bible. But I really have to wonder if the congenital inbreeding of the Egyptian royal family hadn't already caught up to them. After all, lowered IQ's are one of the early symptoms of an inbreeding program.
Enough of my native sarcasm and quibbles.