I would like some advice on which cherry rootstock to use, I have a small garden and would like a cherry tree that can be kept to a size of about 8ft what would you recomend? Also at 8ft what do you think the root system would measure? thank you.
If you are aiming for a cherry tree of no more than 8ft then the Gisela 5 roostock is the only choice, although you might find it wants to get slightly larger than that.
A mature tree would probably have roots with a circumference of about 3ft - 4ft - it could be more or less depending on your situation. You would need a stake for the first 5 years or so, possibly a permanent stake.
You could also consider growing it against a south-facing wall if you have one, as that makes it easier to keep the size of the tree under control and also easier to net the tree if birds become a problem (as they often do for cherries).
Regarding varieties, all home-grown cherries are nice to eat, simply by virtue of being fresh from the tree rather than from a supermarket. Stella or Sweetheart are good choices for most of the southern UK.