I have ridden in Wales and all over England, including the Peak District. I found the uphills to be challenging. I rode up the Holme Moss in dreadful weather (journal entry here). My advice would a) be ready for some hard grinding, b) choose a time when it isn't raining, and c) try to time your ride when the wind isn't too nasty.

When riding there, I have always used the AA maps (3 miles to the inch) to find routing on unrated rural roads. Frankly, I don't find it hard to find empty roads in England and I virtually never ride on bike paths (because they aren't listed on the AA maps!). Of course, there always the CTC routes (and forum).

If you live in Reading, why not try the Chilterns for a bit of uphill? I took the train to Newport and rode north from there (journal entry here) on a virtually empty, though narrow, road.

As for where to park, etc, it seems the CTC forum or a local TI would be useful.