If I read well, you can dodge as frequently as needed. parry, it is -20% cumulative after the first try.
Also, you need a big shield. Otherwise, with a small one, you get hit all the time (or you put a big arm's armour)
For the %age, I say that if you use weapon and dodge, your dodge should improve as quickly as the weapon, as you'll use both of them pretty often.
As for the oarrow, can't we dodge arrows? If so, then dodge them all