we used to buy poults via a local agent from Kelly bronze. Its the best way to buy the right breed for the finished weights. Its getting late now and we used to get ours in July. No different to any poultry really, crumbs then grower then fatter. Its very expensive they eat and eat.
Problems are - weather - could make them very big or the opposite. Most people want 12 - 14lb but if they ask for this and yours are 18lb then you have the problem of messing with the numbers and not everyone wants a huge turkey nor will they pay the odds.
Any illnesses which is obviously the same as poultry. Mysoplasma from wild birds. the fox loves a turkey, fresh pasture as much as possible, straw prices.
They must be hung too. No taste in a straight kill. Finding someone to do the kill and plucking is a complete nightmare then you need a good walk in fridge.
Price - to cover the poult price, feeding, and kill youll be lucky to break even. If you could in the initial buying of feeders, lighting, heras fencing, electric fencing, labour and electric - you'll be at a loss.
£8.00pkg is the bare minimum. Its very very important to finish them properly they must have the right fat, a massive layer of fat is exactly what stops the bird from getting dry and cooks fast (I do mine in 2.5hrs on 18lb er)