One important step to do that will help prevent fertilizer burn is to water your roses at least 3 hrs but not more than 24 hrs before you apply fertilizer & than water your roses a second time immediately after applying the fertilizer. This is extremely important to do with inorganic chemical fertilizers because many of them have properties similar to salt & this is why they are the fertilizer most likely to cause chemical burn. Many of the fertilizers you talked about are organic & are less likely to burn but I would still do this double watering because they are very dry & you need to get them wet so the soil microbes can start breaking them down & realeasing their nutrients to your roses. One last thing, I suggest that you have a soil test done to see what you really need to add to your soil. For example, you are talking about using Epsom salts & this is commonly recommended by many rose growers for the Mg but I don't use it because my soils have adequate to high levels of Mg & maybe your soils have enough Mg also but you won't know until you test your soil.

Bloom Booster fertilizers are high in phosphorous. I wouldn't add both rock phosphate and a bloom booster fertilizer. Actually, I wouldn't use a high phosphorous fertilizer in the first place. Phosphorous is the fertilizer element most likely to inhibit the growth of beneficial mycorrhizal fungi and I think it's true that most older garden soils already contain too much added phosphorous.

If you are going to use a multitude of fertilizers, you should keep track of the total amount of the nitrogen added. Any rose fertilizer label will give you an idea of how much total nitrogen is needed by a rose and you should make at least a rough attempt to not exceed that amount. Remember the total amount of any nutrient added in a season is determined by three factors: the analysis of the fertilizer, the amount you apply and the frequency of the application.

Wirosarian and Mike Rivers have given excellent advice.

In what part of the country do you live? Soils vary with location and not all will require the magnesium in Epsom salt.

It's hard to go wrong with compost, and kelp/seaweed products have always given me great results, as has alfalfa meal.

Being a basically lazy gardener, I just buy a pre-mixed organic fertilizer like Rosetone, sometimes supplemented by a manure dressing or an extra handful or so of alfalfa pellets. That way I don't have to keep adding numbers to see if I am using too much phosphorus, etc. The pre-mixed organic fertilizers also break down more gradually, so there is less problem with fertilizer burn. Unless you really enjoy mixing and matching ingredients, why not use a tried and true organic mix? For me, it simplifies life.

Kate