Is it possible to install Raspbian with all settings as I want them, with scripts and GUI I have programmed and with MariaDB with all necessary tables?
So the next time it boots it is ready as the final unit.
Or do I need to write a script that is run after the normal install?
I do not understand what you want to achieve. At least one time you have to configure the default installation with your add ons and settings. So at the next time it boots it is ready as the final unit. It will not forget all your effort so you do not need to do it again or using a script.
If you want to distribute your setup just take an image from your master SD Card and clone it to other SD Cards like it is done with Raspbian.
If you want to have an unattended setup so that isn't possible because Raspbian does not have an installer program like Debian or other distributions.
