It is really not possible to make a proposal for landscaping just according to the photo, the space must first be seen in reality. Only then can it be drawn in a photograph. But definitely not a rock garden in the middle of the garden! The correct rock must be low and will best stand out near the house, the house can directly form the background of the rock. Do not forget that the rock gardens only bloom in spring, April to June it will be a flood of flowers, during the summer only green carpets. The space must also be filled with other perennials. It is also important to orientate according to the sides of the world and select the appropriate plants accordingly. When choosing conifers, it is necessary to think a few years in advance, from a beautiful small plant you can grow a huge tree that will interfere. I would leave both Sakura and Rhododendron as solitaires in the lawn, just covering the circle with stones and sprinkling with bark. Along the way (just a lane in one row) I would put low bulbs, snowdrops, snowdrops, crocus, ladenky, blueberries, anemones, hellebore. They bloom in sequence as I write them and it will be decorative for much of the year. If you have children, somewhere near the tree (so that there is also shade) it will be suitable sandpit, leave most of the area only English lawn and space for a pool, slide, children will appreciate the children's house, preferably only airy from natural material, the connection of the house to tree trunk.