We highly recommend that you use an electrician to wire a doorbell if you don't have electrical skills. You can tackle this project on your own, but it would be best done alongside a professional to reduce all the safety risks, as working with wires can be dangerous and potentially deadly.

A C-wire connects your thermostat to your household heating and cooling system to provide continuous 24V power. The furnace's transformer converts household electrical current into this low-voltage power to operate the HVAC system's circuitry. In most configurations, the C-wire connects to the terminals labeled "C" on both the furnace's low-voltage terminal block and the thermostat. In some cases, if a dedicated C terminal is unavailable, the C-wire can be connected to the "G" (fan) terminal at the furnace.

Often, you can add extra breakers to an electrical panel. A new breaker can help with new appliance needs, and it’s a common solution when finishing an attic or basement. However, adding extra breakers can’t bring in more amps to your house, so you still need enough amp service to power everything in total. 

Yes, blue wires can be hot wires in the U.S. However, they are less common in residential properties than red and black hot wires. Blue wires are typically used as traveler wires in three-way and four-way switches, as well as ceiling fans. They allow fixtures to be controlled by multiple switches, like when there are switches at the top and bottom of a staircase for the same light.