If you go for the 8 speed hub you'll need...
Hub, spokes, shifter, cable, cog. Maybe better with a new chain too.
Maybe better getting a allready built wheel. Depends on your wheel size.
On a deraileur set up you'll need...
Hub, spokes, shifter, cable, cog set, chain
Might be better getting a allready built wheel. Ussualy cheaper than getting one built.
The narrow chain might fit on your cranks. Have to try it. As some chainrings are quite thin. Have to check if the chainring teeth are ok.
Also your frame will have to be widened for a new hub
If you have small wheels they suit hub gears better.
as they can give higher gears than deraileur gears.
also dont have a mech hanging down near the road.