Hubs will likely be unlocked via golden gears, with levels being little more than a means to that end. There will be enough gears hidden around that you could potentially skip levels and still progress. In the ideal scenario, players would be able to progress through the game by playing only the content they enjoy the most. Global collectibles serve this purpose, allowing the player to spend more time in levels they enjoy and less time in levels they don't while still progressing.
Croc was one of my favorites as well!
In addition to bolts and gears, there may be a token in each level (such as a power core). When the player has collected the token from each of the levels in a hub, the hub's flight level (assuming they are added) can be unlocked. Although, this may be rolled into level completion instead.
There are also some secret, level-specific collectibles planned that don't affect progression but give the player something fun to play around with.
The current plan is for all creatures to be robotic. Some are native to their environment. Others are resource-mining invaders. But, they're all artificial. For example, the scrapyard contains nanomachine-infected zombie robots and pumpkin spider robots.
There should definitely be an update coming soon with the scrapyard level. My original goal was to get the scrapyard out before Halloween's end. There was a lot of AI foundation work to be done that significantly delayed that. But, even if I don't make the original target date, I'll try to get a rough draft into the demo as soon as the level design for the woods section is nailed down.