A drop for a 700c wheeled bike of 75mm would be on the low side of normal. With 26" wheels, since the wheel radius is so much smaller, 45-55mm of drop is going to be the norm. Use a 75mm drop on a 559 wheel and you'll be dragging pedals left and right.

As far as OS tubing, with your weight, I would guess that either a lighter gage OS tube or a 9/6/9 standard diameter tube would be fine. I'd go with OS, though.

Use socketed dropouts. I'm assuming this is your first frame, if this is the case, keep things simple. Trust me on this.

Download and run RattleCAD to design your frame. It will show the angles as you're designing your frame. However, 7* is going to be the angle of the chainstays exiting the BB sockets. I would make sure you're using round or R-O-R chainstays for a touring frame, unless lots of tire clearance is needed (i.e. for knobbies).