Light in details but I'm just tossing this around. Do not worry if it is practical. For an Elementalist, it is quite possible and practical. I'm looking to see if I missed a rule where this would not be possible.
If it is possible, then the effects would need to be worked out. Perhaps just giving a +X to soak for all the elements is the best. Another spell with the same guidelines could be used to ward against magical elemental creatures.
Yes, it's possible. The requisites would add magnitudes to the base (which would be from the highest level one). I would do as you suggested: +X to soak. It's a lot easier to handle that way.
I'm not sure it's so practical even for an elementalist. You would definitely want the duration to be short... well, unless you're using it specifically to kill someone via dehydration. Also, while the spell is active you couldn't carry or use money, use a knife, use a metal knocker, etc., but the magus can probably use spontaneous magic for a few things.
use bone and wood tools instead of metal. Sure you can't carry money but most of the mages that I know have the grogs carry the money anyways.
On the other hand, you do have to be careful if you think it makes you very protected since those archers can still shoot you and quarterstaves and cudgels (easy weapons for thugs) can still smack you around. Bone weapons still can hurt you.
all understood. I'm looking more at what a Elementalist could do. Now I will need to see what is practical. It is not meant for a long term defense because that would be impracticable for the reasons mentioned. Optimally, it would be mastered with fast cast and harnessed to use as a quick defense and be able to drop it at the end.