Yes, you can do it externally but you need external grade cable - normal will yellow and degrade quickly.
If you can use a drill, small hammer, screw driver and able to push then it is easy.
You can get teh cable from FS Cables - excellent service
C5EC has basic weatherproofing or the C5ED has extra external protection. Either should be fine.
It will take you less time than finding a tradesman, getting a quote and waiting for him to do it. Including installing boxes, running cable, terminating and basic testing would take me under an hour (assuming you have a typical 2 storey house).
M H C
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