parti-gyle brewing

[puddin']

I've been thinking about making a sour from the second runnings of a beer. But I need a little ideas, help, or suggestions. My plan is to brew a 10 gallon batch of a pretty basic ipa grain build with an OG around 1.080. I plan to use mostly 2 row, some white wheat male, flaked oats, and wheat. Collect my wort from that and brew an ipa from it. I then plan to collect the second runnings from this spent grain to collect 5 gallons of wort for the sour. Does this sound good? What do you think the OG would be for the 2nd runnings? Should i boil the 2nd runnings? I dont plan to add hops to it, so I dont think it will be necessary to boil. Does this sound good? What yeast should i use with this sour? primary ferment it with us-05 and then add a sour yeast blend? or just ferment it all with a sour blend? Help me out... Thanks