If you buy a complete kit from one source, then it is pretty much plug and play. cable routing is something that can be refined as you go. Using spiral wrap goes a long way to keeping things neat.
If fitting a hub motor then basic bike mechanic skills are all that's needed. If fitting a rear hub on a bike with 9 or 10 gears then wheel dishing can be an issue. However many on here have sorted it themselves and there's plenty of help to be had.
If fitting a crank drive then chain line can be an issue but, again, plenty of people have self sorted.
By going the kit route you end up with a bike you know and understand well. Maintenance becomes a left hand job and, should anything go wrong, the parts are generic and self replaceable.
Besides, I would imagine you've got the time at the moment and such a project would help aleviate elements of stir craziness.