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.

Both suggestions above are good. One house we did had an outdoor deck area which led to a pool and we put timber decking on the deck with a perpendicular timber-decked walkway leading to the pool. We then put lights in the walkway which created a 'catwalk', continuing along the deck. It looked great at night lit up with the pool lights on too! Love the stepping stones and gravel idea too.

a thin layer of gravel in a border of your left over bricks would be quick, cheap and OK to walk on if the under surface is level and compacted..or giant concrete pavers or new railway sleepers could look interesting and re-use as many of the existing bricks as possible to connect with the area outside

Start with a budget and how much you want to spend. Think about how much work you are prepared to do yourself. Think about the type of roof cover you want, and how it will be supported. Think about maintenance, and how often you are prepared to stain or oil a deck. At the top end I would look at a slab to match the existing slab, with a tiled finish over both new and old slabs, with a vergola roof than can open and shut. At the bottom end I would think about concrete pavers laid on a sand bed with pebbles in between and a market umbrella. Middle range would be a timber deck with a pergola and shade cloth. Lots to think about.. Best of luck, Dr Retro of Dr Retro House Calls