Hi trailrat - now there's a few to get us talking!
1. I think so - a bit like people, there's a fine line somewhere between enjoying one's food, and eating until it's unhealthy, and carrying all sorts of health risks. Veg can be over-fed - and grow too fast, too juicy, too soft, etc; and they fall prey to all sorts of pests and disease that a lean, mean veg shrugs off.
Easy to say - but lean, mean, ------- and tough? Like I said - fine lines, here! :)
2. Adding manure/compost year after year makes your soil slightly more acid (good for potatoes); adding lime brings the soil back up to (near-)neutral (good for brassicas). Going the other way - to get a more acid soil - a bit trickier to get something long-lasting, unless you grow the acid-lovers in pots?
3. Can be done
http://www.hdra.org.uk/organicgardening/gh_seeds.htm - unpredictable ("Mama's baby, Papa's maybe"?) depending on how the plant was pollinated. And not worth it with F1 vegetables.
Hope there's somebody who knows more than I do coming along soon!
4. Haven't a clue! :)
All best - Gavin
