Ignoring everything else, I wanted to answer this one:
> 1. Is there a way of saying that some grammar is more complex that others - objectively?
I think so. English verbs, for instance, are significantly easier to conjugate than most other European languages. There's just less stuff to remember.
Another example with verbs is the subjunctive, which has all but disappeared from English (I wish I were, rather than I wish I was), but is still very much required in a language like Italian, even in the present tense: (Credo che sia importante instead of credo che e` importante, which is translated as "I believe it's important").
When you take complexity out of one part of a natural language, it ends up sneaking back in to another part.
English verbs by themselves are easy to conjugate, but English also uses a large number of modal verbs (I did write, he is hacking, we used to travel, she had better shut up) that these other languages lack. So while a native English speaker learning Spanish has to learn a lot of verb conjugations, a native Spanish speaker learning English has to learn a lot of modal verbs, and the special rules for conjugating verb phrases that contain them.
> 1. Is there a way of saying that some grammar is more complex that others - objectively?
I think so. English verbs, for instance, are significantly easier to conjugate than most other European languages. There's just less stuff to remember.
Another example with verbs is the subjunctive, which has all but disappeared from English (I wish I were, rather than I wish I was), but is still very much required in a language like Italian, even in the present tense: (Credo che sia importante instead of credo che e` importante, which is translated as "I believe it's important").