(I only consider the first question) In the first place, I'm not sure I understood the question correctly: what are the two terms of the parallelism? Secondly, I am no sure there is any clear cut evidence in linguistics at all. I only wish to point out that there seems to be a common element in fully alphabetic languages (i.e. excluding those using consonants only or other similar shortcuts): when the alphabet is originally set, it is meant to be phonological or nearly so. (That is less true about spelling, which undergoes revisions when the language has substantially changed, while always using the same alphabet.)

I too am a bit unsure of what this question is about.

There is clear evidence at a phonetic level that lexical stress, sentential contour, and segmental forms are all processed in parallel. Some of these effects can be phonologically significant.

Perhaps nasalizad vowels are the simplest example of two segmental features operating in parallel: the vowel positioning and the opening of th velum - naso-pharynx. A similar interpretation of palatalization, or complex consonants in general, shows two phonological processes acting in parallel.