Just came across this and had a quick read through. South Downs way has 10,000 feet of climbs, we used to ride it in a day back a few years, organised event that's on every year. Some long climbs and descents can be dicey if it's wet, chalk is as slippery as a slippery thing. Not preaching but seat height is best done sitting on the saddle, heel of your foot on the pedal with leg straight is perfect. When you then put the ball if your foot on the pedal your knee will be slightly bent. Tyre pressures off road under 30psi or you will suffer less grip on the front and uphill on the back. I now use 2.8 plus tyres and run about 17psi. Tubeless is the way to go. Less rolling weight and unless you gash the tyre you won't know when you get a puncture.