Am I helping my graduate students too much? As a new university professor, I have been informally tasked with making sure the MSc students in my program are prepared for their dissertations, by prepping them in my research methods course. My students are generally very motivated but they are from academically diverse backgrounds and, frankly, many are ill-prepared to undertake a dissertation and have been struggling with the material and assignments. 

I have been trying to help them as much as possible, but it feels like the more helpful I am, the more they ask for help! 

I have students who express extreme distress and confusion, which I try to allay with more explanation. Then they send me their work in progress, asking me if they are on the right track. 

I want the students to do well, and to feel like they are progressing, but the constant emails and meetings are completely taking over my life. On the other hand, I can see that many of them are just not getting it, and that make me feel like they really do need help.

Is there, in any of your experience, a good point at which to tell students that I cannot help them further and do you have suggestions for wording this without seeming like a bad educator? I appreciate their motivation and I sympathize with their frustration, but at what point do I stop helping and how do I communicate this?
One of the solutions for limiting / demarcating the time you spend on MA students is to set aside specific office hours for that purpose.

For example, you could dedicate Fridays 1p - 5p for the purpose of answering MA questions on theses. If they have questions or if they want to show you revisions of their thesis, then they need to sign up and come to your office hours in person and you would be happy to walk them through things. You need to make clear that the only e-mails you will accept regarding the theses are for signups (or use an online signup system in your course management system), otherwise you'll defeat the purpose of this. 

This serves a dual purpose.

First, it allows you to schedule your life (and balance your e-mail queue). 

Second, it sets up a small but perceptible cost to see you in the eyes of the students. If they know they only have a 15/30/50 minute slot once a week, they will see your time with them as a limited resource in contention with others and try to use it more efficiently by preparing their questions and materials to review ahead of time. In the process, they may answer their own questions.

Of course, you'll want to select time/times that will work for you and your students, but when you chart out your week you should try to set a top limit for student contact hours (and e-mail hours) until you get tenure.