Guesses:
1. One might be confused as to whether the prepositional phrase "with..." modifies the "plastics", "testing of plastics," or "it."

2. That's probably close enough, but more, I think, like "reserve."
The main thing is not to use the same words as a swimming pool (unless it has a similiar connotation in the target language).

3. Well, one might make a cross at the sign of some green object - but it should be "transit the golf course" or "walked across the green field."

4. The actions of the Chairman of the Federal Bank surprised investors, etc., many of whom have jobs on Wall Street. (Something like that.)

5. I've never heard this, but I think it might mean something like:
The person who is devoid of ideas or any depth of personality chatters the most.