Hi JP,
Glad you got the basics working.
As DW and Tony have said though, this is far from the finished article.
If you noticed on my drawing, and I think Tony's too, we never marked the control circuits with a L or N, this was because generally it is better not to use 230V for the controls (unless all controls are staying inside the panel), as DW pointed out too, it is usually much better to use say 24V DC for these circuits, this would have made it much easier, for example to add your floats or other safety/inhibit sensors which may be remote from the panel.
Using SELV for the controls makes it far easier to comply with electrical regs, where sensors etc. are to be used outside of the control panel, also consider seperate fusing of the controls, as well as the heater side of things, there are other things too to consider, such as earthing the metal work of the panel, a seperate earth strap to any doors and/or any removable covers/gland plates, IP ratings of the panel, safety and voltage labels. As you can see the list just goes on and on, and this is far from easy, if not impossible on an internet forum.
As Tony and Dw also pointed out, it is a massive legal can of worms to design and build an electrical panel which will have to satisfy a number of different statutory regs, and pass mandatory general electrical safety tests too, from a legal point of view, when offering such items for sale.
I do wish you good luck with your project, and Iam also sure different people will have many different views on the best way forward (many ways to skin a cat).