Welcome to the dark side David
I would suggest the same as Bblinks did. Having your mag in that range makes it much easier to balance the other 2 while using less. Lower mag levels will give you a seesaw effect when adding the other 2 making stability difficult.
Many of us use IO Sea Salt. It's pretty normal for it to be high Alk, slightly low Ca and lowish Mag.
I dose mag and then ca to my new water before adding it to my tank. Some dose it after adding, and some don't bother at all. So it's up to you where you want your tank parameters to be.
As for what products to use there's the expensive, easy to use liquids and there's the inexpensive powders. Any one you choose is fine.
For now I'm using bulk powders and following Randy's 2-part. If I had the money I'd get a Calcium Reactor and dose mag accordingly.
If you haven't moved in the last 3 years you should walk over sometime for a chat and check out my system