as for cutting discs, i use the dewalt brand only, .055thick with a 7/8" center hole.
they last a long time, a lot longer than any others i have used [and i have tried ALMOST all that are out there over the years], and when they can no longer be used in my 4 1/2" grinders, i made an adapter to fit my air grinders that allow the discs to be completely used up.

one caution though. i do NOT recommend the dewalt discs with the PLASTIC 5/8x11 female thread that directly threads onto your grinder. they have a tendency to spin within the mounting points with just the SLIGHTEST amount of pinch, whereas the basic dewalt discs just chew on through.

just my experience. your mileage will vary.