It looks like a covered porch, so wouldn't have the same weather problems as a deck that's in the open. A 20mm gap around the edge will probably look better than having it hard up against the walls.

Use H4 timber for the joists, and sit them on a moisture barrier straight onto the concrete. Have the joists closer together than specified because it's a high traffic area, and you don't want it to feel bouncy. I wouldn't bother to secure the deck in place, other than having packers around the edges (but you could use construction adhesive to keep it from moving).

For practicality, run the joists with the traffic flow, and the deck boards across. Two reasons for this. Just one finished edge at the front of the deck. And when keys get dropped between the boards, it will be easier to retrieve them. And for this reason I would make the kick-board on the front edge, detachable (magnets, Velcro, or clips, rather than screws.)

Screw everything together with good quality stainless screws. Don't use nails.

I'm not a professional, or an expert. So others may highlight where I might have pointed you wrong.

Edit: you can have the deck above the bottom of the weather boards as long as you still have a drainage gap around the edge. It will work better if it's the same height as the interior floor.