...the socket is going to need to be 1.5mm to 2mm for strength with a key so that the model does not rotate...
I'm not sure what flight stands are already available, but including a key (or an adapter) to prevent the model from spinning around might be a good idea.
As to where to put that optional hole for the flight stand? Well, there are a few choices, but looking at that cargo hook area might be a start.
PoP (Power of Plastic!) and CoG (Center of Gravity):As for center of gravity, yep, that can be a small issue, but this is a light plastic kit, and not a heavy resin/metal kit. So even if a pilot or co-pilot is added, the center of gravity wouldn't be heavily affected [pun intended]. A good flight stand can handle this. Also, hidden counter weights (such as lead shot or small fishing weights) are easy to add to adjust the model's center of gravity - if needed.
Counter Weights:@Rubicon Models - please do not include counter weights with the kit. There is no need since this stuff is easy to acquire. Besides, most modellers have their own preferred method of doing this. For example, one of my favorite methods is using a mixture of lead shot with a little bit of epoxy, and packing the mixture into small hidden areas - as needed. Of course, there are other ways including using simple small lead bars. It all depends on the amount and shape of the space available for counter weights - if needed.