ᐅ Laying and Connecting Patio Pavers: Use Sand or Gravel?

Hello everyone,

we are now ready to build our terrace this summer. We have chosen a concrete slab: 60x30x4.5 cm (24x12x1.8 inches) | Weight: approx. 18 kg (40 lbs).
Our landscaping contractor has prepared the base (60-80 cm (24-31 inches) of compacted mineral aggregate), and from there to the top edge of the finished terrace floor, there are still about 20-30 cm (8-12 inches) remaining, depending on the slope.

In the installation instructions for the slab it says: "Installation note: joint spacing: 3-5 mm (0.1-0.2 inches), base: sand bed or gravel/chip bed."
Now my question is: which is more suitable? Sand or gravel/chip? What grain size is recommended? And how should the joints be filled in each case?

The second question is: How do I best connect the terrace to our house facade? We have a solid house with insulation and plaster. Is it enough to place a strip of roofing felt between the facade and the terrace slab, or should one leave a 1-2 cm (0.4-0.8 inches) gap and fill it with sand or gravel/chips?

I would appreciate any tips.

Best regards,
Sebastian

We have now decided on a gravel bed and will leave a 1-2 cm (0.4-0.8 inch) gap towards the house, install roofing felt, and then fill it with gravel.

Does anyone have experience with joint sealing?
There is supposedly something similar to sand that is mixed with water and applied into the joints, sealing them so that nothing can settle in and no growth occurs...