You can check out the vegetarian bánh xèo version on the previous link.
The longer you let the batter rest the better. It will still be good after 2-3 days in the refrigerator.
I used water to dilute the banh xeo batter, maman sometimes used to add beer (for the leavening agent).
I used leftover grilled chicken, you could use the meat of your choice.
Some people also like to add pickled carrots and daikon to the filling (we don't).
You can buy rice flour at the stores. I prefer grinding my own though. I know all the nutrients are preserved. I use the Nutrimill brand mill. If you cook a lot, this machine might be very useful to make any kind of flour.