Welcome to ATP!
I am far from a grass expert; I can only speak to my personal experience. Bermuda sun/fescue shade combo is what the people who had my house before me did. It works fine if you don't mind a bit different looking grass in different areas.
And yeah if you don't mind it, just leave the bermuda anywhere it will grow. It can be difficult to get rid of due to the extensive roots and runners.
As for weed killer, most products like "Weed B Gon" (sic) say to not seed until 3-4 weeks (at the earliest) after its use and to not use it on new seed until it is well established and mowed at least 3 times.
Here is a link for shade fescue tips:
http://www.walterreeves.com/la...
