I'll preface this by saying that I do use the GH nutes, grow-micro-bloom and I'd say so far it's been awesome and pretty inexpensive. If the botanicare stuff works, then rock on.
But with that being said, I feed every watering. How often is dependent on the size of your bucket and at what stage your plants are. At some times they're growing quicker and need a feeding every few days, and other times it's a little less than once per week. Check your plants every day, pick one up and you'll be able to tell if it's needs water or not. It just takes some time and you'll get used to it. Just check your plants daily and listen to what they tell you.
I don't personally need Cal-Mag but it's a common problem with hempy setups and depending on the strain you're using you may or may not need it. Just keep an eye on it and see if you need it.