You need a book; no one can give you advice on this without seeing, and even if they did it would be irresponsible to do so without knowing how you work. So grab the stone, as much as you can get - you can probably get rid of excess if you end up with it - then take your time reading and planning so you do the job right. Remember that stone can also be bought, probably the same kind or similar enough to blend in. So don't panic if you're a few stones short.

Boston Ivy generally grows by crawling along the ground or up a wall. Don't let it get near your wooden fence in the shade. Propagating can be done in the spring through to the fall. If you go to your friend house and get down and look how ivy grows you'll see that it sends roots out at the leaf node. Prune a branch about six inches long from the root. Combine 3/4 plants together in a soil mixture of manure and sand, add some bone meal and tamp the soil down around the plants. Water. Now if you find enough branches with good roots no need to propagate. Dig the roots up with a shovel, prune back the roots and plant them in your yard. And water. Here is a link that might be useful: Propagating Perennials

bgav, you used the term "sinkhole" but the general discussion does not indicate that a sinkhole is likely. It's probably a hole caused by surface erosion in which case solving erosion problems would take care of it. While slopes can present erosion problems, these are not unsolvable. Usually, all that's needed are groundcover-like plants whose roots form a network that holds soil in place and whose tops protect the soil surface from slamming rain and flowing water. Sometimes it can be difficult to establish such plants (if rain washes them out before they are established,) but it's not impossible if one dedicates one's self to the process. I would consider retaining walls necessary only if the grade is so steep that it cannot possibly stay in place as a slope. Do you have slopes so steep that no planting can possibly hold them? Look around the neighborhood and see if like slopes exist and if they are stabilized by plants. It such slopes exist elsewhere, they can exist on your property as well. You would only need to find plants capable of stabilizing them and working with your overall landscape goals. While the last picture you added is still too close-up, the slopes seen in it do not seem overly difficult. It's likely that if you have plenty of places where retaining walls COULD go, but limiting them to places where they are actually NEEDED might be a better strategy. We would not be able to suggest where such places might be without seeing some overall, wide shots of the areas. If you seek advice about where retaining walls could go from contractors who sell them, it is likely you will be advised to add a lot more walls than you need. Consider hiring a landscape architect or a qualified designer to advise on where walls would make the most sense.

I'm working towards this - http://www.gthomson.us/projects/landscaping/backyard-from-backside.png It's not 100% accurate, but close. I'd like the bigger grass area about a foot higher on the bottom side, but can't figure out how to do that in the design software. yet :-) My question... the edging around the two grassy areas will be some kind of hardscape block wall - only a couple feet in height at most. On the left side of each, I'd like it to flush, or almost flush, at that point. To me, it makes sense to start working on that hardscaping on the left/top side. All youtube videos I see are showing them starting on the bottom side (right side in my picture) - the lower side, and then building up. Am I really screwing myself if I try to build it from higher to lower, or are there ways to do that successfully? To be honest, it actually seems like the more logical way, for what I want, but I've never built any kind of block/retaining wall before.