I'm not a fan of the pre-mixed scary-blue fertilizers. I test my soil in a couple of locations in the spring (dead easy, get a cheap kit, they are not crazy-accurate but they are good enough), then I get whatever I might need to correct a lack of certain of the 3 really important nutrients:

Nitrogen: blood meal. Do not apply when windy, water in when done. Smells sort of bad when applied. Phosphorus: bone meal. Water in when done. Potassium: actually don't know as I've never had a low potassium reading.

I also correct pH for whatever I want to grow. Lime is the usual way to raise it (make it more alkaline) and you can use sphagnum peat to lower it (make it more acidic).

Your best bet is to compost and to get some good sterilized manure mix. Adding these to your garden yearly will be a bigger plus than trying to be a chemist about it -- they will have a yoinkload of the NPK as well as micronutrients that NPK testing and "scary blue" fertilizers tend to ignore.

The problem with putting non-sterilized manure on crops is that you might introduce funky bacteria to the soil. This is usually fine because bacteria that like intestinal tracts don't tend to like being in the ground, but it's a good idea to keep your crops off it; e.g. don't rest your tomatoes on it. I know, this is common sense stuff, oh well.

To be fair, you can totally get away without the testing kit and just adding "stuff" to your garden every year, but I'm a geek and prefer to know numbers and stuff.

There are no health issues from using Miracle-Gro.

There are probably environmental issues due to runoff getting into the water table -- the worst thing that happens here is that fertilizer gets into streams/ponds and causes algae blooms.