easiest is to start with a normal gas powered kart roller... so you dont have to learn kart building.
get a "gasoline replacement" brushed motor.
a matching motor controller.. cheap because its brushed. the controller will have a diagram of the contactor and throttle it expects.
some lead acid golf cart batteries.
cheap home golf cart charger.
then you just bolt the motor in place of the engine.... hardest part is finding the right sprocket.
figure out where to place the batteries.. they're big and heavy and this may be the hardest part of the project if you need some tabs welded on.
wire the controller to the motor. wire in the controls like the pedal and on/off kill.
finally wire up the batteries.
to charge it, use the simple golf cart charger.
this will be fun, and reasonably priced, but not last a long time between charges.
you can make it last longer and be higher powered by running used EV batteries like Volt or leaf modules... but then you need a bit more knowledge, like a BMS... this is better left as an upgrade than a 1st kart.
btw the absolute easiest way to go is to buy a pre-made electric kart, then mod it....but that will more expensive long term.
