I did it last July but carried a tent and wild camped. It took me 6, reasonably leisurely, days, including half days on the first and last days due to transport arrangements. I used packhorse to transport and they were great. it you are thinking of Youth Hostels book early as they do get full quickly.
The reason for me choosing to go self supported was to have more freedom to stop and start when I wanted. The trade off is that I therefore travalled slower and wrestling a bike with full bikepacking gear up Black Sail Pass was a challenge.
I thoroughly emjoyed the experience, the scenery is stunning. I was lucky with Harter Fell in that it was relatively dry. The worst of the route for me was the section from Kirkby Steven to Tan Hill Inn, partly because it involves bog trotting across sphagnum peat bog with no decernable path and partly because I have convinced myself it was ‘down hill all the way’ after the Lakes.
Make sure you look after your feet, mine looked like I had trench foot after the bog trotting and rain.
I intende to do it again but would stay in youth hostels to give me a different perspective.
Enjoy the trip.