Hi Stamford, when you say "chicks" how old are they? I assume that you know they will need to have artificial heat until at least 6 weeks/are fully feathered, even in this nice warm weather?
Sexing chicks is a bit of a gamble, unless they are auto sexing on hatching... see my post on "age old question... pullet or cockerel" lol.
You can vent sex at a day old (for experts), feather sex from a couple of days (certain breeds, especially the heavy breeds, the girls develop longer flight feathers than the boys - whose flight feathers stay the same length as the covert feathers - this is by mms, so you need a good eye!), by 6 to 8 weeks you can often tell by the face furniture (comb and wattles) - boys will have a much larger comb and wattles, and they will be much redder than a pullet - but again, it's not 100%, especially if you don't have another of the same breed to compare against (again see my post
) The most reliable way of sexing is waiting until they either crow or lay an egg I'm afraid - crowing often comes first though, at anything over 8 - 10 weeks.
As to introductions, well, I put my chicks (who were 5 weeks at the time) in their pen and after a week took the pen down so the chicks and hens mingled. The chicks are right at the very bottom of the pecking order, and even after another 2 weeks there is still quite a lot of squawking going on, as the older hens chase the younger ones out of their (the old ones) house, or away from the treat bowls - but my hens have about 120m2 of space, so there are plenty of places to hide, perch, sunbathe etc, and I have 3 feeding stations and 3 watering stations, so no one is completely on top of each other.
Keep in mind that DEFRA states that each hen should have 1m2 of run space, and that this is an absolute minimum... most people try for at least 2m2, and the more space the merrier!