answers for emo duck

That's actually a good set of questions, a lot of it gets brought up in some guides to using the shadow conjuration/evocation lines of spells. Ultimately, there's going to have to be some GM rulings on it, but generally IIRC....

1. Yes
2. The way it's worded here is rather poor. A shadow conjuration wall that you believe in would hold you up, despite only being partially real. (Generally, this is where the GM has to make some rulings as to what 'partly real' means, but this is one of the more common interpretations I've seen.) The fact that it has no mass makes everything more complicated. **For the sake of ease, I'd go with allowing the half-damage,** as that seems to be the intent of the ability and is more fun than saying 'Nope, your quasi-real stuff can't hurt things.'
3. It's entirely dependent upon your ruling for 2, but if you allow damage, I don't see why not.
4. Again, some more GM ruling. If they're capable of doing any harm to your opponent, I'd suggest yes. (Perhaps at a reduced bonus if you want to penalize your shadow caster for some reason.)
5. This one is going to be based on GM ruling. If you let it be based on the bestiary entry, you never know when they're going to summon something niche that is very good at one specific skill check that they need. Alternatively, if you base it upon their ability, it effectively allows them to perform those skill checks remotely. I'd lean towards the latter, but both options could be fun.

Bonus: If you want some extra reading that covers similar issues with the vancian spells, here are two good links:  https://docs.google.com/file/d/0B5kvBvq2DEHjR1dOeEVkRUU4WlU/edit?pli=1
and https://docs.google.com/file/d/0B5kvBvq2DEHjTVF4NEY4SXpSTUU/edit?pli=1