Turkey Avairy?

We currently raise Blue Slate and Narraganset turkeys, we are planning on slaughtering the majority of them for Christmas turkeys for our family members. We do wish to keep a trio of each breed though for breeding next year. So far they have had the run of our 4.5 acre property but we need to keep our breeding birds somewhere safer and prevent them from climbing all over our other poultry's housing during the day. As much as we love free ranging them during the day they are getting up to a fair bit of mischief. We have decided that to build each trio their own aviary.
We're thinking of a 20ft x 20ft space for each trio,which would give them 400sqft equaling 133sqft per bird, 7 ft tall so it's easy for us to walk into them. Where we live it rains most of the year making mud a big problem in most of our runs. We're thinking of putting a gravel down(some kind with a smother surface as not to harm their feet) to help with the drainage. Their coop will be 5ft x 6ft, we'll have some roosts for them and two large turkey nesting boxes. we also plan on putting a kiddy pool dust bath outside their coop with a small roof. They're going to be built beside some already existing runs so we will be able to hook it up to our electric fence system to prevent bears from breaking in.
Is this enough space for them and does anyone see any problems with our design or have some positive suggestions?

Sounds like a plan. Other than thinking through the best method of providing the maximum drainage (any slope, at all?) and a few roosts in the corners of fencing at about 3.5 ft. to hang out on during the day (ours use these a lot), seems your turks will be pleased with the result. We use a folding infant fence to separate nesting/brooding hens from others: