My drain line is 5/8" ID. That allows me to be even on the bubble level without a drainage problem. A slight down slope will eliminate or reduce condensation on the hose if not insulated, but truthfully I have had no problem with a flat exit and no slope of the wall unit.
I replaced a very old 5-ton central ac which used forced air electric heat (42,000 btu's, 14kw) with a 2-ton Gree Terra. It has cooled and heated the bottom floor better than the central ac at a much lower cost (due to better technology and about 30% in-attic duct loss.
I went further and zoned the bedrooms with window ac's and oil filled electric heaters. After the grand experiment worked, we are moving on to put mini splits in all bedrooms to further improve comfort, efficiency, and fire safety.
As an aside, I will note that I completely disassembled the old ac system and ducts myself to reclaim the attic space in my house.
