Cases where both past perfect and past tenses are possible?

Hi. I have two questions on tenses. Help.

1. Would you say the tense after the phrase "by noon," both past and past perfect tense is possible?

eg,

They went to his house and by noon, they had set up (set up?) all the things for the meeting.

2. Are the past tense possible when you have words like "previously" in the sentence? I think if the word "before" replaced the word "previously" in the following sentence, both past and past perfect tenses would be possible.

eg,

They started doing what they had previously stopped doing.