RE: Minimum Power Requirement
Why the expected high weight? There's no way a properly built 1000 sq inch wing of that size needs to weight that much. WIth even a little care it can be made to be around 4 lbs and fly with a .15 to .25 on it. Or is this a load carrying model?
For windy flying you will find that you need more power to maintain flight. The low level turbulence can play havoc on the model and a touch of extra power is all that helps to maintain altitude. I've never studied or thought about why this is the case but I suspect it's got to do with the sudden mini stalls due to parts or all fo the wing being subjected to various velocity variations and some of those will be high drag stalls that may last for just a moment and then you've got normal airflow again. Either way it takes a bit more power to hold a climb or fly level in turbulent conditions.
If it is a load carrier then you can forget about hand launching. There just is no way to throw a flying wing at enough airpseed to be at the minimum from a hand launch.
When you're calculating the lift and thus the speed you need to be aware that a flying wing is limited to lower lift coefficients. In the case of the plank style wings this is due to the airfoil that has a lot of reflex in the camber line to be self stabilizing. IN the case of a swept flying wing this is because the tips are operating at a much reduced lift coefficient that can often be near 0 while the center is lifting its heart out. Again this is due to the need for stability. But it means that less of the wing is actually there to lift the load as some of it is flying at greatly reduced lift values because it's being used to stabilize the pitch moment during flight.
All of this means that you need to alter your calculations for minimum flying speed. My own rule of thumb is that for swept flying wings I figure that only 2/3's of the wing area is actually "lifting" and the other third is there for stability purposes. For plank style wings you can just use the airfoil's maximum lift coefficient. Typically they are down around 0.6 to 0.8 which is a lot lower than many regular airfoils.