Synchronous and asynchronous ways of teaching both have their importance.  Teaching at a high-school level, I feel that the students need "to touch base" a few times a week or they do not get their stuff done or ask questions.  They need the face to face for sure. 

I am learning about Cantasia for videos but it is difficult using new software.

I always provide feedback and go into detail about their answer.  The "why" needs to be answered so students can fully understand a concept.  

I use google classroom: I will make sure assignments are in one spot and that I label each so the students can easily find them. 

I think daily discussion questions due by midnight is a great way to get all of the students involved.  I post the questions in the am and they have all day to answer and respond to at least two other's answer.  I haven't tried weekly discussions but I think if it was a good topic, that would get more engagement from the students.  

When responding to work or videos that I have the students post.  I tell them how they did on the assignment and then I add something personal to the message. 

Organization is the structural key to online learning.  I also think that communication between the instructor and the student is vital.  If a student has a question, they shouldn't be left hanging for days, this will cause increased frustration that doesn't need to be there.