We buy day olds - keep them under heat for three weeks or so, then they go out in to a covered pen in the field. Moved daily to fresh grass. Based on Joel Salatin's pastured poultry system but on a miniscule scale.
Adlib chick crumbs then grower pelets. Kill at 12 weeks, roughly. 3-5kg cleaned weight. We only do one batch of 12 each year, for our own consumption, but it works pretty well.
Wehad poor experience with Ross Cobbs - I don't think they're good for outdoor systems, prefer Sassos or Hubbards