Dont have to use the chainrings that come out of the box, though 26 to 24t is not much of a difference ..
chainring teeth may be a bit thick for 9 speed chain
Universal Cycles -- Sugino XD600 Crankset the spec is 7~8 speed .
the 8 speed Bar end "Ultegra" is the same quality as the One called 9 speed D-A..
probably better to go 40/40 rather than 40/36 since your other rim can be a spare for its damaged mate
36 is common, so the field bought spare wheel will work if you go 36 - 32 or 36 - 36.
BUT.. When people damage a fancy wheel , in the busy summer touring season , the premium hub is handed to you to mail home.
perhaps a steel axle Shimano Hub is more pragmatic as parts are most common ..
Phil's Mud shield fits inside the lock rings and adds a bit more shielding of intrusive grit wanting to contaminate the grease in the cartridge Bearings
IF Going to a External BB a MTB Triple will Offer a Lower Low gear .
Up coming is Pauls Comp cable disc caliper big aluminum Knobs need No Tool at all to turn to wear compensate the Pads ..