Definitely to the Rollrights. Route a work in progress.
I reckon the foyer of New Street Station is probably the best starting place for this one. It works well for the Yorkists (who, admittedly, have a much nicer station), has things like coffee and loos, and I know how easy it is to get lost by bike in central Brum.
ETA: Hadn't thought about cars. Wonder if the MAC car park is okay to use overnight? (Can check..) I was reckoning on following NCN5 through Canon Hill Park on the way out of the city, so could meet motorists there with minimal danger of anyone getting lost.
Sunrise is 6:42 on the 15th. How long do you reckon it'll take you to ride 80 odd km (including a couple of hills), nobby? I'm reckoning on at least an hour of stoppages for the Tesco stop and assorted faffings.