No need to be perfectly exact, because in an outdoor situation, there will be inevitable variation in the soil, the breakdown of the material into a form the plant can absorb, the weather, etc. Your recipe looks reasonable.

Unless you get a soil test and know exactly what your soil needs to grow roses, or whatever you're growing, fertilizing is a crap shoot. Don't get all wrapped up in the numbers.
Ask any five rose growers and you'll get five different NPK numbers.
Before adding Epsom salts you should check if your soil needs it. Most soils have sufficent quantities.
Get a soil test!

I have checked with the UW system for their testing info. Standard test includes:

pH, lime requirement, organic matter, available
phosphorous (P), and available potassium (K).

The are additional tests (available for an additional fee) include: lead, soluble salts, physical analysis, boron, sulfur, manganese, zinc, heavy metals

Am I okay with just the standard variety?

Karl's advice is good, as always. Just one other point: if you do get a soil test you can add to your self-description as right-brained, artsy, and one in a million grower of roses.

Don't add Epsom salts unless a soil test indicates low magnesium. Excess magnesium (or anything else) can be harmful.

Bone meal is pretty much a waste of money. Most soils already have adequate phosphorus, and the mixed organic fertilizer will contain plenty of phosphorus.

Some mixed organic fertilizers already contain alfalfa, others not. Read the label.

I have never measured any fertilizer application and my roses are all big and healthy. A handful of Rose Tone thrown to the left of the plant then another to the right. A handful of alfalfa cubes to the left and then another to the right. The entire process takes about 30 minutes.

Sometimes my hands smell funny.