To "lighten up" regular white flour some bakers will add cornstarch. I don't know if that would work with WW flour but it might be worth a try. Like Pete says, using 100% WW flour will give you a dense product.
For what it's worth, ATK recommends Land o' Lakes butter.
In my experience if you are making something where butter is the star of the show (croissants, for example) the average supermarket product doesn't cut it. Something with a higher fat content is needed (I use Plugra).
Cultured butters are a bad idea for baking - too tangy. Otherwise, as KYH says, go with the basic supermarket brand.
There's all kinds of steamed puddings as you know Brian. Which one are you talking about particularly? I would imagine that with no leavening it would be pretty dense. Ergo, if you use all purpose (plain) flour you would need to add an extra dose of baking powder.
I don't think I've ever really trusted the science of injecting. It seems to me that whatever you inject just fills the spaces between the meat fibers and is likely to be squeezed out when the fibers contract during cooking. Brining on the other hand acts on a molecular level and retains the flavored liquid. I have no evidence to support this theory; it's just my opinion.
No, you are not doing anything wrong. What you are describing with the beans is a common phenomenon. You can deflate the bottom crust after it comes out and to help "waterproof" it a bit more, brush the crust with some beaten egg white in the last 5 minutes of baking.
Pretty much. With liquid fillings there is always the struggle to prevent a soggy bottom crust. Pre-baking helps to remedy this. Generally speaking, you would pre-bake a crust when the filling is liquid or when the filling itself is not baked - like a pastry cream filling, for example.