How will we be able to tell which ships can leave the atmosphere and which ones can't?

The smart answer is trial and error.

I think the easiest way to do that: there's a G-meter on the HUD now, and so if you just maneuver out in space, you can see what the accelerations are. And you would think, oh, okay, so this ship is only accelerating at two meters a second upward. It's clearly going to struggle when I get to Daymar, which is three and a half meters a second.

The less smart-aleck answer is that as resources like the Galactapedia come online, as more information about the different destinations of the Stanton system, and by extension the Star Citizen universe, comes online, just like a normal pilot would have to prep for any journey, you'll have to sit there and say, okay, my route takes me to this and to this. What is the local gravity on that planet? What are my landing options, and what ships do I have that can complement that? The answer is planning. Right now, in the state the game is currently in, that would be a little more difficult, so that's where you get the trial in there. But ultimately, we intend to have all kinds of resources available to you, the Galactapedia, your discussions with other players, to get you the information you need to make the most important decisions in that regard.