In woods and grasslands, everything lives under a mulch where the top layer is undecayed and the bottom layer is fully decayed (2+ years old) and releasing nutrients. This is a good model for the gardener. However, it sounds like your yard man is overdoing. Typically it is recommended to maintain a mulch 2" to 3" deep. I guess, though, the situation is something like sheet composting or "lasagna gardening" where people pull back a deep layer of compost and plant at the soil surface or a couple of inches above that. So if I had that situation, I would plant roses there and see what happens.

You certainly don't want any lawn/turf grass growing right up to the base of the plant - that's just a maintenance nightmare. For a truly 'natural' look, the plants should be connected by a single planting bed rather plunked down individually directly into the lawn or even with a small mulched area - that just looks random and disjointed. FWIW, mulching is the best thing you can do for your soil and ongoing plant needs so I would encourage you to get over your aversion to it. If you just can't tolerate the mulch, once the shrubs are unified/grouped into a single planting bed, you could underplant with a groundcover. This link will give you some place to start but there are many, many groundcover options available. Check online or at a better local garden center for selections suitable for your growing and light conditions.

Yes, remove it. It is not a valuable tree - it's basically a throwaway in the nursery industry. All prunus are susceptible, some significantly more than others. You can treat with a fungicide and a lot of pruning, but I wouldn't bother with a purple leaf plum. If you're looking for a spring flowering tree, consider service berry (amelanchier)

Jena, my Perle d’Or did the bud drop thing it’s first year, the whole year. A lot of my roses also had chlorosis, including Perle d’Or, even though they were getting regular Magnesium-sulfate and I was alternating between Miracle Grown and a seaweed fertilizer, all in the hopes of curing them of chlorosis. Mostly it was the Polyanthas and Multifloras that had this problem. Finally I sent in a sample for a soil test. I had plenty of all the minerals and nutrients except for Nitrogen (which I already knew since its obviously devoid of any organics and so I was fertilizing) and absolutely zero Manganese (Mn) detected. Once I put a teaspoon of Manganese Sulfate dissolved in a gallon of water on each rose last fall the chlorosis completely disappeared and Perle d’Or stopped dropping buds. I will now do this once or twice a year; not too often since Mn is a minor nutrient and too much can be toxic. The Miracle grow I was using did have trace Mn, but somehow it wasn’t enough. I wonder if my soil was just binding it up? This just demonstrates that bud drop could be due to lack of an essential nutrient. It might not necessarily be Manganese for you. But since you mention the Kellogg soil might not be that great, I would give it a nice dilute liquid fertilizer once a week and see if it cures it.