Need help planning my gardens...

We bought this place a couple of years ago, and I only got started last year. I have several challenges that I need help with. The style of the house is kind of Dutch farmhouse( or maybe it looks more like the barn?) Overall, I have sandy soil, with a lot of rock in it. Because I have large pine trees, the soil is acidic in a lot of areas. In this climate, we consider it to be muggy when the humidity gets into the double digits, so I can't plant anything that wants evenly moist soil.

I have the areas planned where I want flowerbeds, but I don't know what to put where. I love those cute garden plans with the circles that tell you what grouping of flowers is where, but I can't seem to create one.

1. I have a corner of the yard, framed by chain link on two sides, full sun most of the day. It is a triangle shape, roughly 10' on each leg. Last year, I had moneyplant, both purple and white, coneflower pink and white, purple penstemons, purple catchfly,yellow strawflowers, red and pink dianthus, moonbeam coreopsis, and lemon thyme. And yes, it looked just as hodgepodge and bad as it sounds. Some of that I didn't plant there, it just grew! Heights were a problem, with the wrong things in front.

2. I have 3 HUGE pines in the front yard, against the fence, under which no grass would grow. So I started circular beds under them, with 3 different tiers. I planted some hostas, (which promptly died), persicaria red dragon on the fence, (which didn't do really well, maybe too much wind and not enough water?), bleeding hearts, cinquefoil, red valerian, jacob's ladder. Only the cinquefoil and bleeding heart really thrived.

3. My third big problem area is another corner, where I have an older than dirt elm tree that is 2/3 dead. (Cannot afford the money to have it removed) Soil under it is quite rocky, and hard to dig, but it can be done. Nothing wants to grow there, definitely not grass, even weeds look stunted. Suggestions?

I am giving myself some money to spend on the garden this year for sanity's sake, and I have a really good variety of seeds, other than what I have already mentioned. Have a long list, I just have not had the patience to get it loaded. I need a plan of what to put where. Do I need to post pictures? Help!