If you have access to a sand blaster I would do that for sure price permitting of course. Find one with no liner at all and skip the entire step if you can.
I put my first grate 22" above the fire and added one above it about 6" higher. The top one is not far from my flat lid so it is limited to what I can put on it like ribs or something thin.
I would also suggest putting a set of hardware below your cooking grate for an additional lower cooking grate in case you want to put something under your meat to keep the drippings off the fire. I prefer the taste without the drippings hitting the coals. I just throw a piece of foil on my lowest grate and poke some holes in it. It seems to stop enough of the juice falling on the fire.
Good luck, you will love your UDS.