To scale up thrusters you can simply make them bigger, but that leads to a lot of wasted space as the thrust is only produced by a ring-shaped region of the device. To improve thrust density, you can nest these inside each other (see this page on my research group's website https://pepl.engin.umich.edu/project/high-power-hall-thruste...). More recently, we have been looking at running smaller thrusters at higher power densities, which was previously impractical due to the way older thrusters shaped their magnetic fields. Nowadays we can design thrusters such that very little power is lost to the walls so high power density operation is looking more feasible.

Per the second question, you would need a very efficient thruster to limit the amount of mass needed as propellant. If you have an entire planet, you might look into using a photon rocket. Alternatively, you can try a massive solar sail or magnetic sail but I'm not an expert on these things.