Taking these a few at a time (and writing to teaching situations as I understand them to be in the US):
- course staff needs to be notified prior to prolonged absences
- course staff cannot doubly-educate/train students who are behind.
- TA meeting/zoom time is for understanding learning objectives previously covered, not private lectures/tutorials for catching up due to missed lectures.
These are OK policy-wise, but have no teeth, or a penalty associated with enforcement (your last item notwithstanding). What do you do for the students who inevitably just don't choose to go along with this?
For the second item, rigorously publishing and adhering to your prerequisites should largely address that, but there will always be cases where students who have passed their prereqs still don't understand the material well enough to thrive in your course. Welcome to post-secondary teaching. It may not be your responsibility to teach them that material, but in today's teaching environment, where you can scaffold a course in multiple ways without doing much work, you at least owe it to the students to tell them how to catch up. Also, it would be wonderful to communicate to the teachers/departments teaching and grading the prereqs when the students don't understand the material in courses that they got passing grades for -- but this may be a matter for your department chair to diplomatically take up.
If by "behind", you just mean that you don't want to simply repeat lecture material for students that don't come to lecture, yes, that's frustrating. Perhaps you can just add an attendance requirement to the grade scheme, and make it worth enough to have teeth. Alternatively, you could make your lectures available on video. Yes, I know that has impacts on attendance, and nobody likes lecturing to empty rooms. This is an issue many of us deal with. The most success I've had with this was to personally manage access privilege to each lecture, with students who needed access for legitimate reasons emailing me with their excuses. This is marginally more work for me. Also, COVID isolation policies forced me to abandon this plan, but those are going away. It felt manageable when I tried it, though, and I believe I'll go back to it.
For the third item, write it down all you want to, but it remains up to you to train the TAs how to deal with such situations, or it won't make any difference what you actually write down.
- students with a score below 50% by week X will be recommended to drop the course.
My own opinion is that this is unwise. Curricula and requirements are very complicated things. Depending on what your course is, and who needs to take it to graduate, this action may have many unpleasant unintended consequences -- for the students, for teachers of "upstream" courses, for your department. I'd urge you to discuss this with more stakeholders before simply implementing it and letting the chips just fall where they may. I've seen policies like what you'd like to implement in action, and had a ton of very real problems with them. The way it worked for me, as an academic advisor, was to receive a list of students who were told to drop an important engineering prereq (an some of the letters the students received were really poorly worded and demoralizing), and it was essentially a list of underrepresented minorities that I advised. "On-ramp" issues for certain students are very real, and need to be identified and fixed. My own attitude is that if our admissions department is accepting students, then we owe those students every effort to thrive, and excluding them from classes doesn't meet that goal. In the case I encountered, my reaction was to go to the Deans with my observation, and tell them that if we couldn't find a better way to resolve this, that I would be following up with a civil rights attorney on behalf of my advisees, as these students were being separated from 4-year STEM degrees in ways that might not have been fair or necessary. In response, we found a better way to identify these students before they found themselves in trouble, and to move them through a slower sequence of prereqs that would give them a real opportunity to hit full speed and still graduate in 4 years with an engineering degree.
While I know the situation you're trying to fix is right up there with the most frustrating things a post-secondary teacher can encounter, I don't believe that your policy can really fix things.
It would be much better to formally warn students in this situation that they are very likely to fail the course, and let them make their own decisions about what action they need to take. It would be Much, Much better to identify those students very likely to fail before their failure (or forced withdrawal) is carved in stone, and help them to identify what needs to be done to pass. It would be much, much, much better for your school to find a way to deal with on-ramp issues more effectively, and this involves the professors that notice them making a bit of noise.
- an incomplete grade will only be given when there are 3 or fewer missed assignments (not exams).
This seems like a reasonable policy on incompletes. I'd probably try to word it better, and pop it in the syllabus, and make sure students hear and understand your incomplete policy on the first lecture day. My personal preference would be to provide the date certain by which grades of incompletes must be discussed, leaving an "out" for students with true last minute dire emergencies.
- students not in compliance with the above conditions will receive a grade based on the total score at semester end
This need not be said. In fact, EVERY student should be graded the same way, which is how you say the grade will be generated in your syllabus. Adding a line like "missing items will receive grades of zero" should be sufficient.
My own preference is to not write a syllabus as if students are expected to find themselves in trouble, or for those students likely to find themselves in trouble. Write your syllabus to let every student know what is acceptable behavior in the course, and hold them to it. My personal opinion is that until you know the students, they all deserve the same answers to the same questions, and that not doing so is letting confirmational biases work their way in to your processes, and that's sub-ideal.