Yes, the demo ends after the turret section (the result doesn't matter). There are preview builds that will have more content and they are available through discord server -> https://discord.gg/FFwyf4n
There is no full game yet.
The tinker aspect is available in roguelite mode. Note, it is more difficult mode in many aspects. Less energy dispensers, more complex navigation, if you die, you have to restart - from outer rim, you don't have to go through the intro.