I'd say dont use more than 20% of the feed as whey, at least at first. Then that way you can see what effects it has on the pigs.
I've looked up some basic info in my Animal Nutrition book it only gives whey in dried matter form (pig requirements will be aimed more towards commerical, but these are their basic requirments, so shoudnt make too much difference to the majority of breeds):
Whey needs of pig 50-90 kg Sow pregnant sow lactating:
DE (digestable energy): 1mj/kg 13mj/kg 13mj/kg 13.5mj/kg
CP crude protein: 106g/kg 175 g/kg 120-140g/kg 150-180g/kg
Lysine: 9.7 g/kg 10.0g/kg 4.8 g/kg 8.0g/kg
Tryptophan: 1.9 g/kg 1.4g/kg 0.7 g/kg 1.4g/kg
basically the whey lacks a lot on its on, maybe even start with 10% and then work up to 20%, if you have good maths skills or a ration formulation programme you could work out exactly how much.
I don't think anyone would add more than 20% fruit and veg to the diet (as in to be a main part rather than use grains and legumes/soya), without having consulated someone with pig nutrional skills .