Great questions! I am predominantly a materials scientist, which means I work at the other end of the distance scale with atoms, but I will try to point you to some resources that can explain more about black holes without going too much into the math.

A black hole is a region in SpaceTime (these become axes of the same space in General Relativity) where the pull of gravity is just so large, nothing, not even light can escape from it once past what is known as the 'event horizon.' It arises as a mathematical singularity, which is like a divergence of SpaceTime. (If you have ever plotted 1/x, you'll notice one such singularity at the origin where the function diverges.) Physically Our current theories about black holes tells us that once stable, a black hole has three independent physical properties: mass, charge, and angular momentum. What happens when you put a black hole near other objects in the universe?

a) Whether a black hole is able to "suck in" another planet has mostly to do if that planet is near the 'event horizon', which is the area around the black hole where nothing can escape from its clutches. The radius of the 'event horizon', known as the Schwarzchild radius, is dependent on the mass of the black hole. A larger mass means a larger Schwarzchild radius. Beyond this radius, the black hole looks like any other object with the same mass (and one of the other two independent properties). So it is entirely conceivable that a black hole could "eat" an object much larger than itself. In fact, this is been observed with system known as Cygnus X-1