E-mail works well for this too. I have no problem with people stopping by, but the odds are that I will be hard to find for most cold calls. The same probably applies to the TAs. This is a serious class, and will require a significant commitment of your time. Expect the lab preparation to take about 3 hours week.
Attendance is taken at recitation.
You may go over your homework, or confusing parts of the lecture or lab with your TAs. You may even use the recitations as group study sessions with the TA present if you wish, but you need to be there. I think that is a little harsh, so will give you an option. I will make photocopies of the documentation and store them until final grade reports go out, then they will be destroyed. Documented field trips can be excused if I am notified at least 10 days in advance.