when should i start them off
I've already started mine as I was a bit late last year.
do i have to keep the potato whole or is there any benefit cutting it say in half
I leave mine whole but others cut them up. I think the potato keeps making more shoots until its exhausted. If this is the case, the bigger the tuber the greater number of slips produced
i know that you pluck the slips off and root them do the roots that grow fatten up into tubers big enough to eat ie the sweet potatoes
The slips grow into plants with an extensive root system. On these roots new tubers develop. If the weather is better than last year yes they should produce edible sized tubers.
how do i know they are ready?
Leave them to grow for as long as absolutely possible. Tubers develop late but the longer they are growing the bigger they will get. By the way, I found that it was no use trying to have a sneaky look as the tubers develop quite deep down.
I'm trying to do a page on my website but all there is there at the moment is a few pictures so I'll deny you the link.