Hi Harry and welcome to the forum.
First of all, how many hens do you intend to get, and what ages and breeds? Most people start with POL (point of lay) pullets, which will be around 16-20 weeks old and might be expected to start to lay at around 22-26 weeks, depending on the breed, once they've settled in. If you would like to post the link to the coop your wife has got you, we could perhaps advise about how many it will comfortably accommodate - which may not be the same as what the manufacturer might have claimed, it's very common for chicken coops and runs to be sold with unrealistic numbers of birds in mind.
If you had to keep the birds in an 8ft run all the time, there would only be room for two, we recommend a minimum of 2sq. Metres of run space per hen minimum, as overcrowding can lead to fighting and other problems. However, as yours are going to be lucky enough to have plenty of field space, it willbe OK to just keep them in the run at the end of the day and in the early morning , when there will be most danger from foxes, provided you don't keep too many in there at once. The trouble is that when a new group of hens arrive, there is always a lot of competition for the top positions in the flock, and until they settle down, one or more may be bullied and will have nowhere to get away if confined in a small run.
When they arrive, I would put them in the run, with food and water, and leave them to explore and settle down. Some people put them actually in the coop and close the door, and if you could collect them late in the afternoon, this might be a good thing to do, letting them out early next morning after they've slept together in the coop. But if they arrive in the morning, they will need food and water before bedtime, so in that case it would be best to leave them in the attached run for a day or so, before letting them out into the field.
What sort of fences do you have round the field? Many poultry keepers use electric fence, not only to keep the birds safer from foxes and other predators, but so they can section the field, using one part whilst resting the grazing in the other sections. If you can do this, you could give them a smaller enclosure round the run to start with, whilst they find their way around, which would be better than confining more than 3 to the run, and also better than letting them roam the whole field at first.
