Before you get too deep into the project, you might want to calculate the time required to heat up the bed based on size, material, and power applied. See: [
jscalc.io]
In general, it's not a good idea to use DC power to heat the bed, especially if it's 300x300mm or larger. A heater doesn't need DC or regulated voltage, so it's better to use AC switched with an SSR. You won't need a big power supply or fat wires.
Ultra MegaMax Dominator 3D printer: [
drmrehorst.blogspot.com]