I agree that you should be fine with the pitch from a single yeast pack.
I personally would slightly increase the Special B quantity and cut out the crystal 40. It'd be more in line with the style. Special B provides more of the dark fruit flavors that are key to a good dubbel.
I would also use more dark sugar. Either D-90 or D-180 would work, but I would use more like 8 oz (since I'd normally use at least a pound for a 5 gallon recipe). Definitely don't skip the dark sugar--that is absolutely key to getting the flavor profile right. It tastes different from darker or crystal malts--much more dark fruit and marshmallow flavors. If you don't use dark candy syrup/sugar and instead use only dark malts, you just wind up with a weird Belgian-ish porter.
You can also use some simple sugar. Good attenuation is key to the style, and sugar helps, whether it's just table sugar or candy syrup. At the same time, 1.069 is not so high, and with your yeast, you'll probably get good attenuation no matter what.
I would not do a secondary. Just keep the beer in primary for 3-4 weeks, see that the gravity is stable, and then conduct your conditioning in bottles. Secondaries are good when you're making big additions (hops, wood, fruit), but you won't be doing that here, so it's just a chance for oxidation. (Autolysis is not a concern with Belgian yeast in a 7% beer.) And you'll have plenty of time for conditioning in bottles.