Can you substitute soy milk powder for soy flour?

Soy milk can be used instead of milk when baking, but one has to make some adjustments. Regular milk has natural salt; not plain soy milk : minor adjustments may be needed. Then, there are flavored...

yes

I have used soy as a substitute for regular milk, with success. You need to be careful as it bakes up a little differently and you may notice some 'cracks' in your pumpkin pie, but it stills tastes...

Well just use normal oil and flour. If you really need something close, get a different type of oil and flour. Like olive oil.

Try watered down marmite, it really works!