I agree with Jubal - use a GFCI breaker or outlet.
It was much easier than I thought it would be. I would say 3/10 (fairly easy) including the furnace R&R.
I removed the furnace but would not have had to. If you do you will need to dis/re connect the thermostat wires and gas line. The only tricky part is reinstalling it - need to align the vent. I did it alone but a helper would have made it easier.
I pushed a piece of 12-3 romex from the driver side dinette past the bath. If you remove the furnace it is easy to catch it. If not get under the bed (fun) with a flashlight and an assistant and reach in under the fridge. IMHO the best tool for this is a fiberglass fish rod designed for fishing electrical wires - Klein Tools 15 ft. Splinter Guard Glow Rod Set-56415 at The Home Depot
. The cheapest tool is a thin piece of wood trim or a piece of romex. (The romex is barely stiff enough and I recommend the wood trim or fish rod.)