Grit, I'm assuming crushed granite grit, is used mainly to add weight, and dry out a mix, as grit holds no water. It's structure is good, nice and angular And it doesn't break down. Not often used anymore, except to make a mix less water retentive.
Peat moss, this is a tricky material to use. Most commercial peat, usually from Canadian sources, is milled to a fine powder. This fine powder does not allow air to penetrate, especially after a couple years of use. If you sift a bale of Canadian peat, maybe 5% will be greater than 1/16th of an inch. The rest should be mixed into the vegetable garden. In the EU, if you can get German peat, it tends to be much more coarse, with less fines, a better addition to a mix than the finely milled Canadian product.
However, I have medium hard water, with near 200 ppm calcium, so peat is an excellent additive for acid loving plants. If I use peat in a mix, I try to repot every year, or every two years. This frequent repotting will help counteract the tendency of peat to have poor air penetration.
I would consider adding fir bark to your mix. It to will help with creating an acidic mix for azalea, and will hold it's structure for several years, 3 to 5 years.
You can use fir bark with or without peat. Myself, for azalea further along in development, I use no peat, just fir bark and pumice and kanuma. Yes, for near finished azalea, I spend the money on kanuma.