Nothing you will ride in GB will prepare you for climbing for 20+km at 6~12% in temps in excess of 110deg. but hey don't let me put you off
Don't worry about campsites they are numerous, cheap, generally clean and well equipped.
Can you do it? depends on your mental attitude, pain threshold and pig headedness, oh and a bit of luck from the wind and weather gods. Because you have a deadline, take contingency cash and your drivers license, worse case scenario if you are only 1/2 way come the Friday catch the train or hire a van.
Will it be worth it? Yes it is a fantastic sense of achievement, especially overtaking roadies on a fully loaded tourer when climbing a col!
Train, then train some more, then find a hill and ride up it constantly with overloaded panniers, or if you can afford buy a vr trainer and practice on real cols.
One piece of equipment I would recommend (regardless of the fashionista) is a 3ltr bladder pack, no worries about having to fill up bottles every other hour, and no worries about trying to stop or grab/replace a bottle when wobbling up the steep bits.
ps see my sig