I understand the thinking behind using an Austin rose for the form. In warmer climates, his roses tend to be nearly climbing. I think you'll find increased disease resistance and more dwarf, continuous blooming habit benefits of using a greater number of miniatures in your breeding. Personally, I would shy away from using any of Austin's varieties which contain genes from Conrad Ferdinand Meyer as they have a great tendency to rust in warmer climates and are very prone here toward climbing growth. Golden Angel has a large dose of Wichuriana genes, giving it a higher degree of disease resistance in our climate, at least. It also produces a more dwarf plant that is always in bloom.

To illustrate, I created parallel lines of breeding using Basye's Legacy. The first seedling was Orangeade X Legacy and was introduced under the name of Dottie Louise. The second is Lynnie, which was created using Moore's Torch of Liberty, a product of Orangeade X Golden Angel. Lynnie is a more dwarf, continuous blooming plant then Dottie Louise and is greatly more disease resistant than Dottie Louise. The difference between them is the inclusion of Golden Angel. I honestly think you should consider engineering in the desirable traits you can obtain from the minis from the foundation of your line. Kim