This may depend on the particular research community. I can say, at least in spoken presentations in a workshop or conference, many communities may find using 'get' just fine... but many other communities would not.
I would personally like to avoid 'get' in formal writing, I guess you mean research articles. To be sure, you should try to check if the community you belong to uses it in their literature. But, if its for emails or blogs, it maybe alright.
The easy answer is, no. None of the first sentences are correct, except for the first sentence in the first set.
This I have seen and heard regularly. The rest of the sets, numbers 2 and 3 are correct.
Edited: 11 December, 9:25pm EST
I have searched and searched, but have not found a single source that will allow for any wiggle room under the Most High Law of Subject-Verb Agreement. There is never considered a subject, so the subject is, of course, the collection of objects on the table, and regardless of how they are listed, it is a plural subject. I have no grammatical foot to stand on, hence Newton's Law of Universal Gravitation applies.
However, in usage, I will plead my case to Psycholinguistics, wherein research has generated theories in abundance about the architecture and mechanisms of sentence comprehension. At what point in reading does information become available to the reader? Issues such as "modular" versus "interactive" processing have caused heated theoretical rifts in the field.
Sentences are read in separate modules with which the reader interacts. but which have limited interaction with each other. While I generally hold to an interactive theory of sentence processing, in this case I am admitting that the modules are not playing well together at all. In an effort to avoid tedious squabbling, one grabs hold of the first module and deals with its behavior, whilst allowing the others to run amok. Admittedly this is poor parenting on the whole, but what's a person to do? One can listen to the cacophony only so long before becoming overwhelmed.
I place some of the blame on the misbehaving modules. Perhaps it is genetic, as a module does not come into a sentence as a tabula rasa. If the modules would cooperate and line up nicely, there would be little problem.
I summarize that the allocation of attention and the misbehavior of the modules makes this an impossible situation, one that defies the Most High Law. I throw myself on the mercy of the Court.
John Q Public is the Judge.
Best Answer
The second and third examples are more formal than the first, and slightly more suitable for use in a “formal letter”.
All of the examples are acceptable in conversation. In a formal letter, one probably should use more-precise wording. In particular, “need to”, “at least”, and “day” should be clarified or differently expressed.
For example, “need to” might be expressed as any of “The terms of your contract require you to ...”, “I'd like for you to ...”, or “You will benefit more if you ...”. “Day” might refer to a workday or shift, a calendar day, etc.
“Do at least this much” might mean “On average do this much”, or might mean “Never do less than this much, on any day”. For example, one might write “You are required to respond to at least 100 messages per shift, on average” or “You are required to average at least 100 messages responded to per shift” or “During each shift you must respond to at least 100 messages”, depending on intended meaning.