You can fine information about this market easily by Google. Therefore, I will focus only on two things you may not fine it by Google. The first is pray room, then Halal food.
I spend one hour for searching “pray room” at this huge market. Just to share,
First, look for clock tower (big one because there are many small clock tower. See picture of Clock tower).
Second, near to that clock look at soi 16. you will see big Halal food restaurant.
Third, cross that soi 16/7 till the next side.
Finally, on next side go to soi 23 you will see “Kah Jak” restaurant (see the picture). Near to this you will see the pray room but you have to be very focus because it is not so clear.