Installing a privacy fence along the back property line, I would think, would be a must (I like privacy, too!). The concrete slab is an odd thing to deal with. I would connect it to your deck with some stepping stones or flagstone pathway to tie it together. Perhaps on the back 1/2 you could install the lattice panels with vines growing up. That would give you a sense of privacy without feeling boxed in. Using part of that slab for storage is another idea. I never have enough outside storage. Since you want to take part of your lawn out for flower beds, I would get a plan for the entire yard before starting anything. Take your lawn and decrease its size by drawing flower beds around the outside perimeter in large curves, and try to incorporate a portion of the slab and deck areas, too. This will also help tie everything together as well as cut down on mowing. This can also increase your privacy with large shrubs/trees in your plantings. I think making sure you have a complete plan before starting is the most important thing.

While you can change pavers without destroying the invividual pavers themselves, it's a bit of a fantasy to think that you can do this easily. Installing pavers takes a lot of preparation and it's messy and costly. A professional quality installation, making changes, is not something you can do in a few hours on the weekend. That said, pavers are usually prettier than plain concrete, are durable and make a great patio surface. The key to not worrying about changes in the future is thorough PLANNING before you build. Pavers is what I have in a back yard about the same size as yours and I love them. However, there is NOTHING that is "maintenance free." Pavers need an occasional pressure wash (as would concrete) to get rid of algae, mildew and grime. They need blowing off in order to keep free of leaf and grass bits.

For eight people and some spillover, you probably need a patio in at least the 350 or 400 s.f. range in order to accommodate dining, lounging and the outdoor kitchen without it seeming cramped. The S.F. will depend on the actual furnishings, amenities and the degree of spaciousness required. A larger, more spacious patio will seem more luxurious than one that is cramped or tight. A little extra space can accommodate extra people should there be occasional parties or such. You will be linking driveway access to house and pool. In order to accommodate all features needed, a patio might span the full width between pool and far side of house. Then a paved walk might link that block to the drive. (We don't know the scale of the plan so can't measure anything.) You'd want to decide early on whether the patio will abut the house or if it will be set a few feet from it, in order to allow for foundation plantings which could make the patio seem like a friendlier, prettier, more hospitable place. Plants are outdoor decor and they take room. If you want foundation planting between house and patio I would not make the bed less than 6' deep. You'll want to decide if some shade will come from a small tree (not too close to the pool) or if it will come solely from built structures. If any of the shade will come from covering that is attached to the house roor, you'll need to decide that up front and determine how that covering could interface with the roof. It would simplify matters if a roofed structure was not attached to the house.

Just own experience/opinion - grass will grow poorly under that many trees. For kids, bark fines or relatively fine wood chips, mix in compost or whatever if you like for more of an earthy feel. If you want something to grow there, experiment with different cheap seeds or ground cover plants. I say 'cheap' because with kids running about, a lot of it will get trampled, and will depend on local conditions a lot. I've used white mustard, clover and various other odds and ends including mixes of flowering plants. None of it thrives under trees but provides some colour and variety, some have established themselves. For proper plants/bushes, ask around, go slowly until you can figure out what works; sometimes you might be better off with a container plant with good conditions rather than having it compete with the trees for resources. Somewhat depends on the trees - I have norwegian maples and they're competitive b**tards, their roots don't like to leave much room or nutrients for anything else.