TL;DR: Instructors have many responsibilities that they need to balance in order to be successful in their careers, and it is often not feasible to reach out to each student individually. So, rather than reaching out to each individual student, I suggest you make your students aware, collectively, of additional resources, and really be available for those individual students who want the additional help. For those lower-performing students that don't want the help or don't seek it out, they will fall behind and will need to do some much needed soul searching about why they are in the course in the first place.
To answer your question, we need to answer another question first: "acceptable" with respect to what?
Assuming the answer to the above question is "with respect to my other responsibilities," then I would say that, no, it is not acceptable to reach out to every student individually (especially in your case, having 70 students at present).
When instructors need to balance their teaching and other responsibilities (such as research, service, or, in your case, your full-time job), reaching out to all students collectively is the more efficient approach; this is accomplished by making students aware of additional resources that are available (e.g., office hours or additional interaction times, as needed, practice problems, etc.). I list all of the resources available to my students in my syllabus, and I make it a point to reiterate what the available resources are verbally throughout the semester. I also send emails to groups of lower-performing students to suggest that they make some time to come in and talk to me about things that are unclear.
Now, the individual students who really want additional help will seek it out. So, what to do about the students that don't seek out the desperately-needed help? Again, from time to time, I will remind students that help is available, but it is up to them to seek it out.
I suppose your stance on how to handle this scenario may be field dependent. In my field (engineering), I think that engineers-to-be should be "trained" in such a way that encourages them to take responsibility for learning and getting to the bottom of things that are unclear to them. (Perhaps in other fields, such a stance is not as important.)
I have especially noted that, in the follow-on courses, where the topical coverage is more advanced and at a deeper level, students who don't get the memo on how to take their studies seriously and take full responsibility for their learning are really not able to keep up; so much so, in fact, that the course pace is slowed down to the point that I am not able to cover all of the topics that one would nominally expect to cover. This is especially troublesome for the students who do put their best foot forward and are having to suffer the consequences because some of their classmates cannot keep up.
Thus the free ride of having the instructor do every little thing for the lower-performing students has to end at some point so that only those students who are willing to put in the effort are allowed to advance, and those that don't need to do some self reflection and try again.
