First, most fertilizers - even those manufactured from synthetic (chemical) ingredients - can hardly be termed "caustic". Often unnecessarily applied and frequently overdone, they still do not contain properties which would cause a caustic reaction to either the plants (unless you were to pile them on), wildlife or yourself and your family.

Is it a necessity to fertilize? Typically no, but roses are heavy on the nutrient uptake although if they are performing well under the regime you have followed - not a bad one, btw - then additional fertilizing is not a requirement.

Complete organic rose fertilizers are pretty common. They are slow release by nature and it is generally suggested by rosarians to apply them about every 6 weeks through the growing season. Whitney Farms and Dr.Earth are a couple of local brand names. Terrosa is another choice - developed by a local rosarian, it is a single application organic rose fertilizer. Apply once in early spring after pruning and the roses should be good to go.

Although my roses this season are no example, I generally fertilize in much the same manner as you - mulching with compost and my alfalfa application takes a short detour through the digestive system of my bunnies before hitting the roses. Sometimes, if I have the time and remember to do it, they will get a second application of either the bunny poop or a handful of organic fertilizer after the first main flush of flowers. They are not exhibition quality by any means but for the most part - this season aside - they are healthy and bloom well and heavily with this program.

Soils vary, you really need to have a soil analysis done to have any kind of reliable starting point. (A property near me is a mound of sand on a shelf of clay, an example of how dramatically different soil conditions can be encountered even on one lot).

Generally fall is the best time to fertilize hardy plants, whereas early spring is a comparatively poor time.

Sounds like you're on the right track. If you're a coffee drinker then
throw the used grounds on with the alfalfa meal, it works great for me.