I would guess to say first signs of illness would be drop in feeding; ruffled feathers; droopy head; respiratory signs; sneezing coughing mucus; lethargy; separation from the flock. out of the normal behavior. things like that. hope this helps.
don't feel helpless you have a big support system of a lot of people who care about you here! if you ever need to talk or just need someone to listen just pm me. I'll be here for you. I know how you feel. I see so many emergency written here I've become almost paranoid over my birds wondering...
depending on how much they eat yes its perfectly normal. sometimes when my birds are on pasture some birds crops are full some are not
it just depends. hope this helps ease your mind. best wishes to you! they sound completely normal to me. :)