I wouldn't worry too much about supplies as you hit a town every few days.
Hebden Bridge,42 miles,all major supplies.
Gargrave,70 miles all major supplies.
Malham,77 miles, post office and general supplies.
Horton,92 miles,cafe and shop.
Hawes,108 miles, all major supplies.
Keld,120 miles possible farm shop.
Middleton 140 miles.all major supplies.
Dufton 162 miles,?
Alston,182 miles all major supplies.
Greenhead,200 miles,garage and shop.
Bellingham,225 miles,all major supplies.
Bryness 241 miles,cafe and pub.
I have never sent parcels on the PW,only did it once on my first walk,the Coast to Coast in 1982,sent a jacket,three pairs of spare socks,a second pair of boots,dehydrated meals, and five cylinders of gaz to the PO in Richmond,right next door to a camping shop!