Yes, you'll be free to move but must return to within 10 feet of where you entered
From the description of the Ready action in the PHB or the Basic Rules:
First, you decide what perceivable circumstance
will trigger your reaction. Then, you choose the action
you will take in response to that trigger, or you choose
to move up to your speed in response to it.
Moving to the Ethereal Plane is certainly perceivable, so it works as a trigger. As per this QA, there is nothing about being in the ethereal plane that prevents you from taking a reaction.
As for limitations on movement, the DMG has this to offer on the Ethereal Plane:
A traveler on the Ethereal Plane is invisible and
utterly silent to someone on the overlapped plane, and
solid objects on the overlapped plane don't hamper
the movement of a creature in the Border Ethereal.
The exceptions are certain magical effects (including
anything made of magical force) and living beings. This
makes the Ethereal Plane ideal for reconnaissance,
spying on opponents, and moving around without being
detected. The Ethereal Plane also disobeys the laws
of gravity; a creature there can move up and down as
easily as walking.
So you can move up to your speed, you can move through any solid objects, and you can even fly, but you can't move through other creatures (or force effects). Unfortunately, Blink stipulates:
At the start of you next turn, and when the spell ends if you are on the Ethereal Plane, you return to an unoccupied space of your choice that you can see within 10 feet of the space you vanished from.
So you can spy through walls with Blink, but you can't travel with it.