Garden house - Preparing the ground

Hello dear community,

we want to get a garden shed and are currently planning the base. I have attached a picture of the shed as well as two sketches with a top view and a cross-section of the base. Unlike in the picture, the second side of the extension is closed. The shed and the underlying beam are made of spruce and would be painted.
For the foundation, we want to use 6 screw foundations about 55 cm long, which, according to a friend who is a structural engineer, are sufficient in terms of load and wind for this approximately 700 kg shed.
As a floor, we want to lay terrace slabs, and we would build it classically with 20 cm of gravel/crushed stone, 7 cm of grit, and the slabs.
Around the shed, we would lay a about 20 cm wide gravel strip as splash water protection.

And now the exciting questions :)
1. Could less gravel possibly be enough for the floor structure since, for example, no water gets on the slabs thanks to the roof?
2. I would like to do without a solid boundary (curbstones or aluminum strips) between the gravel edge and the surrounding soil for cost reasons. Then gravel and soil might mix slightly, but I do not imagine that to be a big problem, right?
3. The terrace slabs would be limited by the beams. Where the extension is open to the front, I would take long curbstones but, due to effort, preferably not concrete them in. I have read that you can also stabilize them well in soil/gravel without concrete. Hope that’s true :) I had also initially thought about aluminum or stainless steel strips, but they would have to be quite thick on top so that you don’t cut your feet if you step on them... :\
4. The beams that rest on the screw foundations and on which the shed will be built would be in contact with the gravel. Is that okay or bad because of moisture? Otherwise, one could maybe let them protrude 1 cm above the gravel, so that the slabs still rest against them from the inside. Is that doable or too fiddly?

Do you have any other exciting suggestions for me?

Thank you very much :)

7cm of gravel seems like a lot to me. Usually, 3-5cm is used. At this point, I am not quite clear how you want to bring screw foundations and slabs together without conflict. According to the sketch, the beams also lie on the slabs, then they will be in moisture below and will rot. Painting is not enough. It would be more sensible here to have a proper substructure with an air gap above the ground, and then a floor on top of that. Basically, you also have to expect that rainwater will run from the slabs into the garden house.

Regarding the questions:
- I wouldn’t save on the substructure. 20cm is not much and water can also come from the side. Especially in covered outdoor areas, it will rain more frequently
- Gravel strips always with edging, otherwise the next heavy rain will muddy the strip
- You can stabilize curbstones in compacted crushed stone. Drainage gravel is typically 16-32 and not well compactable. In any case, you can hardly compact a narrow strip.
- see above

Basically, your combination of screw foundations and slab floor is neither one thing nor the other. If you are going to go to the trouble of laying slabs anyway, you might as well make a proper slab foundation. Or else, with a substructure and floor on screw foundations, let it hover above the terrain.

PS: under no circumstances take 28mm boards, better 44/45mm planks with double groove