We did the same thing last year. We were told to do the look but no touch introduction when meant we needed a second coop. We started just by having the two coops near each other. One flock could be out in the yard at a time. Eventually we put had the two flocks in the yard at the same time...
First thing is that expect your Rhode Island Reds to come to the top of the pecking order with your birds as they get older - ours are always picking on our other birds. The other thing to keep in mind is your climate. We had our birds inside until at least 8 weeks - but we live in the PNW and...
Rhodies are an aggressive breed. Your chickens will establish a pecking order. Your australorp is coming in at the bottom of this pecking order. The same thing happened in our flock. The first year we got 3 Rhode Island Reds and 2 Sapphire Gems. The Reds picked on the gems (who are bigger...