The campsite on the river bank at Symonds Yat is part of Wyedean Canoe Centre http://www.wyedean.co.uk 01594 833238.
There are not many campsites in that area, There is a Forestry Commission site at Bracelands which is within walking distance of Symonds Yat. If you are walking back in the dark do make sure you know where you are going as it is very easy to get lost going through the trees, especially if you have been to the Saracens Head and enjoyed their Old Peculier.
Re: Daily mileage down the Wye. Really depends on what craft you are using, height / flow of the river and how much effort you want to put in.
If you call the guys at Wyedean Canoe Centre they will give you distances and times and can arrange travel / pick up, for a fee of course.