Hi there,
Yes, there is: devsupport.flightsimulator.com. The SDK team monitors those forums and actually answers help questions over there.
We collapsed the SDK category back down to one category and left it open for people’s convenience, but the real SDK party is over there. 
I haven’t seen it yet, but that is the goal. You will check it out and then check it back in when you’re done. We will not be able to add custom models. I am hoping that that feature will be added in the future.