Analysis first, then plan, as Tookoo recommends. Use native plants, as neotoma recommends. Get specific plant recommendations locally, as Terri & sgelade recommend. Here is my two cents worth, for the shortterm. a. Remove and stockpile the lawn edging and most of the mulch back against the fences. b. Take a can of spray paint, or a bundle of surveyor's flag, and mark the largest circular or curved form that will fit within the fenced areas, no matter where the trees stand (inside or outside of the line) to form the temporary edge of your lawn area. See if the entire family agrees on the alignment or just do what looks best to you as the Senior Gardener. c. Add the wood edging to the new edge, or, it will look a lot better if the edge is not visible, using a steel edge whose top edge is down just above the grass roots and no longer visible, and not an impediment to the lawn mower. (when you form the plant beds, you will dig down a couple inches at the edge, where it meets the steel, and then slope the bed up from there, and the mulch will be contained at the level of the lawn, beyond) My recommendation, after you call in your landscape advisor, is to fill the beds totally with ground cover, beneath the shrubs, so no mulch will be seen after the two years of plant growth, using only a finer textured mulch which will become part of the soil bed. (Maybe the bark mulch will smell good in your new fire pit, along with the wood edging.) d. Plant the entire area with grass seed or sod and enjoy the beauty. The curved edge will make the space appear and feel larger and will decrease the maintenance of the smaller bed areas. On the subject of tree placement: analyse first, then plan. Look at all the views beyond your fenceline from all windows of the house, the living/ dining areas, all the bedrooms, to enhance the good views and to block the big, the bad, and the ugly. The large trees on your list will block views from the upper windows, The small horizontally branched trees will be a piece of sculpture in your downstairs view throughout the year, while their flowering and fragrance yet another reason to be alive. For instance, if you have an attractive small tree that has attractive flowers and foliage, PLUS has attractive bark color and has a sculptural quality in the off-season, you won't have to visit the museum quite as often, with a sculpture garden right out your window.

It is all relative to the entire property, the house and the yard. Is this a part of the pedestrian circulation or a seating area? Are there utilities adjacent, is it in the front yard and viewed by neighbors, or part of your private space. Is it viewed from the dining/living rooms or just from the bedrooms. Will it be used by tricycles or just feet (no golf shoes please). In my experience, (don't you hate it when someone starts off a sentence in which he offers advice with that phrase), the mondo grass is too large for any pedestrian pavement. There are a large variety of more prostrate plants you can walk on at your garden center, I expect. Some can be walked on daily, and others less often. Some are evergreen, some have attractive flowers, some are into more gray or smoky colors than just green. You can mix them up, just as you do with groundcovers in your plant beds. Enjoy!

That looks like it. Some call it crazy paving. It usually gets laid over compacted paving sand/s. The joins between each flagstone are usually concrete with the edges concreted so it stays in place. I have seen some with sand between the joins which also looks good. New sandstone from Gosford Quarries looks superb but is expensive. (its a great product!). I'd look for some second hand stuff on Ebay/Gumtree/etc.

Both options are valid methods of construction. Using a concrecte base is called a Rigid Pavement and does provide a more solid and reinforced pavement structure. It allows you to mortar in your pavers and achieve a very accurate and neat finish. It also allows you to lay thinner tiles, slate or pavers on the surface layer as the strength is provided by the base. It is a more expensive method however. Laying pavers on crushed rock and a bed of sand is called a Flexible Pavement. The weight load is distributed through all the three layers to provide stability. The surface layer needs to be thick enough to be bound together by sand. Therefore your pavers would work in this method. The downside is that you often don't achieve the crisp lines, or the longevity of a rigid pavement. Over time it could settle and move unevenly. Most landscapers I work with recommend paving on a concrete base, however for the pavers you are using, I suggest that it isn't neccessary.