Logs/stumps should be great. Looks like you have a tree in one corner, that provides a bit of a break as well. Tubs, it depends - are they opaque? If you don't mind ruining them (well, as working tubs) you could cut 2-3 openings at the bottom of each one so chicks can dart in and out if they need to.Would some tubs and logs work? I have lots of those.
You don't do quarantine after they've been off the property?I will get pictures. The rooster and hens are at my county fair this week. They will be back Sunday. Should I just wait to add the chicks until all the chickens are at home?
Really hard to say what will happen when the other chickens return, as you're looking at a possible 3 way integration at that point.