Mostly questions dealing with prepositions?

Hi. For no. 1, I believe I asked a similar question in a thread in this forum that has not been answered named "Seems to be problem dealing with prepositions" as its number 2 question.

1. Which is correct? I think normally we would write "I feel relaxed in a room or (either) at/in an office."

A room/an office which/that you feel relaxed (in??)/good (at??) is ...

2. Would you say the following sentence/version with the preposition "up" is incorrect? Or would you perhaps say the preposition "up" is unnecessary (perhaps - optional?) in the sentence/version below?

Chop this vegetable (up??) into fine/small bits.

3. Would you use the word "as" here?

(talking to another person who asked a question)

You asked me how I would write the sentence "Chop this vegetable up into small bits." I would write it as "Chop this vegetable into small bits" without the word "up." if you asked me.