Those are all great questions. I'll go through them one at a time.
I am in 7b which I believe is similar to Washington D.C. (but that may not be right).
I'm not entirely sure what kind of soil we will have at our field, but at our home, our soil is essentially totally silty. Actually, I'm having problems with drainage and my plants getting nutrients. I can tell because many of them have chlorosis on the leaves and new growth. However, that's another topic. My father-in-law planted our garden, so I had no say in preparing the soil.
When it comes to soil for my breeding roses,I'm planning to start with them in large containers, so I can essentially create whatever soil I want. Once we plant them in the ground, I plan to use raised beds, so I should be able to also create a decent soil. Of course, I need to first do a soil test in our field, but like I said, I haven't been able to yet.
When it comes to rain, I'm not entirely sure how to describe it. I'll have to get back to you.
At this point, I'm planning to breed initially for garden roses, but there is a chance that I'll do florist roses in the future. It's not my plan for now, though.
Thanks for the questions!