We add what ever we get our hands on to the soil.
What I have been doing the past 2 years or so... for the ideal perennial planting. I till in Peat Moss, Compost and Mulch. Get all that good stuff mixed together......the mulch will break down over time but in the mean while.........I have about 6 inches of prime planting mix, mulch mixed in keeps the soil lose.
After planted we top off with 2 inches of shredded mulch (black or cedar)
I have never mulched my beds for winter....Personaly I would not waste the money......and no way customers here would mulch late fall/early winter.
Now as far as right plant for the site.......There is no where on any of my properties that are in full sun that would have a drainage problem........Usualy drainage concerns are shade and north face of buildings and or fences. Most perennials that work in shade are water tolerant
In reality not such a hard thing to work out.
My own beds this year.......I am not mulching at all......I have mulched every spring for about 5 years......What is there now I realy need to mix it up a bit and let it break down. This will be the 3rd time I am doing this.....what happens is the quantity of the bulk in my beds becomes more than I prefer and I have to let it break down and allow the volume to settle.
Commercial properties.......I have taken the approach that the highest profile areas get a freshening up of mulch every spring...but the rest of the property gets done in halves every other year......This way I insure that they have the budget and that the entire property is getting mulched.