"That" and "this" are commonly used (somewhat vaguely) to refer to the whole idea in the previous sentence or paragraph, so it is not surprising to find that the usage in this sentence is also somewhat imprecise.
Q1 "of" not needed here as "that" is non-specific: using "those" instead would refer specifically to "rates"
Q2 "That" in the second sentence might be construed as referring to "rate": so "of", "for" or "in" would work. Absolute parallelism not necessary for understanding here, although in general it is a good idea, and often taught as such.
That said, the questions are good ones; it is just depends on what type of document is being written. If this is for, say, a university paper and precise language is important, I might go with "those of the US in total" and "the same as that for the US as a whole".

It depends on what you are writing. In a legal document one might spell it out unambiguously as "between forty percent and fifty percent". Elsewhere omitting the first percentage sign may well be clear enough.

There is a good explanation of mixed conditionals here:
http://random-idea-english.blogspot.co.nz/2011/02/more-on-condtionals-third-and-mixed.html

If I remember correctly, there is a comment in Michael Lewis's "Lexical Approach" (1993) that in conditional sentence one just uses the appropriate tense and modal. If we construe "would" as a modal subjunctive indicating a counter-factual situation, and "have been" as a perfect infinitive indicating the situation is in the past, then this does not sit well with the time adverb "today".

However, I do believe that in some areas, such as Quebec, usage may be different, so there may be some wiggle-room here.

@Berend "but" comes from the same word-root as "buitan" (outside) in Dutch; and in English (and Frisian) also means "apart from". So "she all but died" really means "she did everything (all) apart from dying.