Our terrace is also about 7 x 4, and then it continues with a structured bed and planting into another 4 x 4, but for us, it is excessive, meaning: we could have done without it and simply placed two deck chairs on the lawn or similar there. So: on 7 meters, you can already fit a whole host of people.
Our daughter also has a corner terrace and married into a large family. On one side, there is the grill and dining table (2.40 meters long), on the other terrace side there is a mega seating lounge. During visits, most people do not sit permanently in their seats, there is movement playing with the children, going to the buffet or grill or inside to work in the kitchen or the senior table inside for those for whom the weather is never good, and then there is the fire bowl terrace. Additionally, a beer garden set is set up there where it is seasonally nicest. So on the lawn. What I want to say with this: you do not need a terrace that holds counted seats for every possible family member. Also: in the extension of two terraces, that is where they meet at the house corner, usually no one sits because such a place is usually not the coziest. They have structured planting there now, but with a transition of the terrace. Basically, what you do in the interior with walls and furnishing — giving structure, creating rooms, setting seating areas by planting — also applies in the garden. What takes the least work in the garden are shrubs, bushes, trees. They structure, provide protection from view, wind, and rain. Children’s toys belong on soft ground, lawn, play sand. Lawn and paving require the most work. The area in front of the bay window does not make sense to me because people like to sit in corners. In the planning, there is also no such wide area between the bay window and the main terrace. Whether you even go out from the bay window is also a question. Is it really the case that you cannot get from the kitchen into the garden? Regarding roofing: ask the building authority! But you don’t have to roof everything. Those who sit in the garden also want to sometimes have it open in nice weather. It is good to consult when you buy some garden magazines. Google searches or Pinterest often show just the same thing, plus now there are expensive AI-created versions that don’t fit into one’s own budget. Also, one should not hesitate to draw everything up and furnish and plant it to scale. Usually, nothing good comes from nothing.
It would be nice for the forum and the participants if you could give some feedback on the other questions as well. For example, many people put a lot of effort into the partition wall to the neighbor.