>>1
Basically,「BよりAのほうが[adjective]です」means "A is more [adjective] than B", and 「AはBほど[adjective]です」means "A is as [adjective] as B".
However, this usage of ほど rarely appears in its simple form. Rather, it is often used in conjunction with negations.
For example, "Kagami is more beautiful than Tsukasa" translates as:
つかさよりかがみのほうがきれいです
If you want to negate this sentence, that is, to say "Kagami is not as beautiful as Tsukasa", you can say:
つかさよりかがみのほうがきれいじゃないです
Although this form is OK and often used in practice, it is potentially ambiguous, in that it allows an unintended interpretation, "Kagami is more non-beautiful than Tsukasa."
Instead, the preferred way of expressing negated comparisons is to use ほど. Then the above sentence becomes:
かがみはつかさほどきれいじゃないです
>つかさよりかがみほうがきれいです
"Kagami is more beautiful than Tsukasa".
>つかさはかがみほどきれいです
"Tsukasa is as beautiful as Kagami", but sounds a bit awkward. I would say
つかさはかがみと同じくらいきれいです
>このがくせいのえいごはあのせんせいのほどじょずじゃないですよ
"This student's English is not as good as that teacher's".
>このがくせいのえいごよりあのせんせいのほうがじょずじゃないですよ
"That teacher's English is worse than this student's". Another interpretation "That teacher's English is not as good as this student's" is possible, but I find that the former interpretation is far more likely. I can't explain why.
>>4
The use of ほうが doesn't sound unusual to me. Also, if I used は instead of ほうが, I would put it at the beginning of the sentence, thus:
かがみはつかさよりきれいです
And if I started the sentence with "つかさより", then I would use ほうが instead of は.
This is perhaps because introducing a new topic with は in the middle of a sentence is avoided as far as possible, but this may be wrong. I'm a native speaker, but not a language specialist.