You have MANY questions in this post which would take volumes to adequately answer. Rugosa roses are very disease resistant and are deciduous, they shed their leaves in winter. Most modern roses such as Hybrid Teas and floribundas you're likely to have available to use for your breeding are ever green. Mixing deciduous with ever green roses generally results in the loss of much of the disease resistance in the first few generations. What I'd suggest is to use miniature roses. I know, you don't WANT a mini, but take a look at Ralph Moore's "Linda Campbell". It's a cross between a Rugosa and a miniature, and it is NOT pink, nor is it miniature, AND it's quite disease resistant.

I'd suggest using minis such as Golden Angel; Torch of Liberty; Cal Poly or Joycie. All of which are Ralph Moore miniatures. You could also use Anytime, which created Linda Campbell. All of these are available from Sequoia Nursery, Mr. Moore's nursery, which is one of the sponsoring nurseries for Help Me Find. Using a miniature can easily engineer in a more dwarf, bushy, continuously blooming plant than you're likely to get should you choose a larger rose, such as a Hybrid Tea. You're also likely to obtain a higher degree of disease resistance when using a miniature. They're generally based upon China roses which are fairly clean in many climates. You don't say where you live, so I'm not sure how cold hardy you wish to have your rose be, but minis can also result in quite cold hardy roses. My own rose, "Lynnie", is a cross of a species cross with Mr. Moore's mini, "Torch of Liberty". Lynnie is far more cold hardy than the mini and is tremendously disease resistant. She continues the deciduous nature of the species hybrid; has larger blooms than either parent; blooms continuously in most climates; and has combined the more dwarf, bushy habit of the mini, taming the large, climbing habit of the species hybrid. Lynnie is about a 3' X 3' bush. So, you see, you can get all of the characteristics you seek by using a miniature for your crosses. It was minis, in Mr. Moore's capable, imaginative hands, that brought mossing and stripes into modern roses. They're also being used to introduce the desired characteristics of many species, previously unused in breeding, into modern roses.

There's no telling what colors you're likely to obtain from using any of these minis with your Rugosa. Mr. Moore used Cal Poly with one and got a pale green, thornless hybrid, which has sported (mutated) to a brighter yellow. Think about using minis. With all that's behind them, they're really a mixed bag. You'll have many more possibilities than you can imagine in just one, small plant. Good luck!

I forgot to add, Lynnie is so good, I gave it my favorite Aunt's nick name. Kim

Could be a mutation, a rose "sport", this happens, look if  the cane mantain this characteristics.