The first year I used Easy Grammar, I bought the teacher's book just so I could be sure we were doing things "right". It is more than just an answer book though, it does give lots of tips and information, things like "don't worry that we haven't covered this yet, it will be covered later", explanations of the methodology, etc.
The teacher's book does have the student sheets. Usually, the two pages facing each other are the student blank sheet and the student sheet filled in. So you could use that to make a copy for your student to use, or even for them to write right on it -- so long as they don't peek at the other side. ;)
(I should note that I *assume* it's still this way, the teacher's book I bought was the previous edition, several years ago).
Anyway, once I had the hang of it, I just bought the cheaper student workbooks for the following years.
Daily Grams isn't necessary, it's just different. In the main book, you're doing a topic at a time and just practicing things about that topic, with only occasional reviews. Punctuation is covered in distinct and separate chapters. That sort of thing. With Daily Grams, everything is reviewed all the time. Each page is a collection of exercises from different areas of grammar -- punctuation, capitalization, usage, etc etc. They're supposed to be quick, like 5 minutes to do the page. If you're wanting a really full grammar program, you might do a page of Daily Grams as a warm-up, then dig in to the Easy Grammar lesson for the day.
I didn't use the Grams when we were using the Easy Grammar texts, the last thing my son needed was MORE grammar exercises lol (even though he really did enjoy EG). After a few years of EG, though, I considered the next level and the amount of repetition (reviewing previous years' work etc), and decided for that year to JUST use Daily Grams. There were really only a few "new" topics and they were things I could explain to him easily enough. Otherwise it was just more challenging applications and practice of topics he'd learned already. So the Daily Grams was sufficient for that year.