Posted: 24/06/2016 at 17:24
How big is your greenhouse? Even a dwarf peach/nectarine is going to grow to about 4 - 5 ft and, unless they have vastly improved the cultivars, I believe that the yield for such compact trees is very low, and may not be worth the effort (you would have to hand-pollinate the flowers, for example). Perhaps your ambition is a little too much at such an early stage with your greenhouse. You could research other fruit (melons?) and find it less difficult and more productive.
There may be others who more direct experience, but I have always been led to believe that these fruit trees do best on a south-facing wall (which retains warmth) and I'm not sure that a GH would be the best environment.
Just had a second thought - what about a vine? Lovely grapes, take some looking after, but worth it!