I have started each and every nano with substrate from my 100 gallon and LR
from it as well as 1/2 the water. No problems, ever with this method. If you only use the LR
and water, it may take a bit of time, but not very long. Mantis are tough animals. I would not worry too much about it in your case.
I dont think they are jumpers, but I could be wrong. Best to ask someone who has one. I would make sure that it could not climb up the LR
and get into trouble that way, pump intake, climb out of tank, etc., because they will climb all over the rock in search of food.