I'd love to see an entire thread devoted to hand pollinating and how to choose good parentage. I'm a rank beginner at anything like that; please tell us more! I'd love to try it.
Kristine Albrecht wrote the book on dahlia breeding and covers hand pollinating in detail. When she visited us in 2011, Margaret showed her how she did it. Most all of it is in the book.
When we plant, should we think ahead and try to put potential parent pairs near one another?
“Poor mans hand pollinating “is one plant by another. It does not work all that well. Part of the problem is incompatibility and the two varieties may never cross. We plant types together three 50 foot rows of balls and Mbs and Fds . Several rows of waterlilies. And so on.
2) Does allowing seed production on some blooms of a hand pollinated dahlia slow down flower blooming on the rest of the plant? No way.
3) What's the best way or ways to ensure that you mix the pollens from cultivars you want hand pollinated, and what is the timing for covering or protecting the hand pollinated bloom? Read the book as these issues are covered in it. Mixing is the wrong word as you are hand pollinating and Kristine Albrecht uses brushes. There is a lot more to it than that.
4) where do we find out about good parentage and combinations? I like the idea of making spreadsheets for this type of information, available to members.
We no longer use other peoples named varieties for breeding with few exceptions and use our own multi generation varieties for breeding. Most of them are “private” flowers that we do not share. Any list we would provide would be ancient history.
And of course, the age old question: why is pollen spelled with an 'e' and pollinated, pollinator, and pollinator all spelled with an 'i'? Spell check sorts it out.
The most important hint: make sure you are growing varieties that make seeds as many or most do not. 
