Earth gives you a stupidly wide margin of error, where the Moon gives you none (and Mars very little) - because of its dense atmosphere. Landing on a world with an atmosphere means there is a passive force that tries to get you stop (relative to the surrounding medium). So, as long as you survive the hell of reentry, you can help yourself with lifting surfaces and parachutes. In contrast, on the Moon, you have to zero out your velocity at exactly the right moment. Do it too late? Crash. Do it too early? Crash. Run out of fuel just a little bit too fast? Crash.
It's less unreasonable than you think. The Ranger 1 spacecraft attempted to land a payload with an impactor before the US had figured out how to land more carefully.
Dumb laser distance measurement should solve that easily for you. You can literally use some very basic math with thruster output based on your downward distance/speed.
Sure. The problem is delta-v. If you zero out too late, you crash, but if you zero our too soon, you'll likely run out of fuel and either crash or won't be able to take off or otherwise complete the full mission.
Managing delta-v is half of what makes a Moon landing require precision. An atmosphere can let you ignore this half to a degree (depending on specifics of vehicle/mission).
With 1/10 gravity dust also goes quite a lot higher. That's on top of lack of atmosphere letting dust float higher. Not to mention, there's going to be a lot more dust to kick up.
Anyway, the easiest way to get a feel for these things is to play some Kerbal Space Program. Try doing some moon flights. You'll quickly realize that the part of the mission that feels easiest on the home planet (landing) also feels the hardest on atmosphere-less bodies, and vice versa (e.g. taking off, or slowing for landing).
