Small amounts of substrate has never hurt any of my snakes so I would not worry about that.

As for tank agression I beleive it is a MYTH I have an older snake 2-3 years 1100 grams who was a rescue I was told she was very tank agressive that is why they wanted to let her go. She has been fed in her enclosure all her life from what I have been told and I would beleive it. She was very thin and hungry when we got her and damn hungry. Which is why she was hunting and striking ate anything warm in her cage. So I have been feeding her approperiate size F/T in her tank for 2 months now and well she has no signs of tank agression UNLESS I smell like a rat. So the easy fix is dont smell like a rat. I can get her out and handle her minutes before feeding while rats are thawing in the room. Easily move some of the features out of her cage while the rat is laying on the counter next to her cage. The second I hit the rat with a blow dryer game on the yes she is agressivly looking for food and well if I get bit it would be my fault she is in hunt mode and my hand is warm. Sorry to rant but I am a little tired or hearing about cage agression as a mater of fact the only time I have been bitten is while trying to take a BP out of a feeding tub after feeding becasue some holistic pet store idiot told my wife that you can't feed in the tank because of cage agression. So feed in your enclosure it causes less stress for the snakes and makes your life easier.