ET20 for 8" rims is about right with 50mm spacers on the rear and none on the front. You can always add some thin spacers at a later date if you want a wider stance, 5mm spacers are only £7 for a pair so fairly easy by trial and error to get what you like.
As for tyre sizes about 24" diameter seems right, you will have to play with a tyre calculator online to find the appropriate tyre size for your wheels.
If you have a search through the threads like this one you will see what others have done
http://www.madabout-kitcars.com/foru...highlight=tyre