"finish it up" doesn't sound natural to me in this context. "finish it" seems more likely. "OK, let's go and finish it" implies that you are going to a different location to finish it.
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Wonder123Yes the speaker is the most important person who takes the decision, and his assistant are giving him some kind of suggestions and looking for his action.The question "We would like you to help us complete this project" is not very likely to be asked of someone in that position.