[susan53]

We talked about these word here. it's the same ...

1. They'd be more usual in written than spoken English, but aren't particularly formal.

2. No difference in meaning. If by focus you mean emphasis or "weight" - information in a subordinate clause tends to be less important than that in the main clause. So in (a) the ideas have roughly equal weight because they are both in main clauses, whereas in (b) the first piece of information is clearly subordinated to the second.