While figuring out a better way to implement them you could just make them easily craftable for testing purposes. A cool way to acquire them could be that on a spawner destruction there is a modest chance to get a new one, I would also make them craftable but fairly expensive in therms of technological advancements (Maybe requiring a flying robot frame)

I also wanted to suggest to give the personal assistants regardless as the game is new or not, I know it is possible since I've seen AAI vehicles giving the starting miner even on pre-existing saves, maybe asking the author of that mod or looking into it could give you some inputs. https://mods.factorio.com/mods/Earendel/aai-vehicles-miner

I hope this was useful, bye!

Definitely by some kind of a structure you craft - especially if you plan on making them robot-like

hmmm I guess it's different depending on the skin. Maybe I should just use all the skins and have each available in different ways. i.e. Bots have to be crafted with advanced tech, biter "eggs" dropped from spawners and then researched / harvested into a pet biter.

Still plan on making a humanoid skin as well.

I saw the humanoid skin in the drop-down. Is it not actually available as of the latest release?

Right. It's just there as a place holder for now.

There is a "cat" skin already that is out there and in further development with more animations. I'm friends with the author who is about to create a robot (possibly Dalek) skin. Seems there "could" be some synergies here. His was to just replace the biter enemy entity.

I'll take anything I can get. I have zero graphics / art skills.

maybe each skin and corresponding goods can be under it's own tech? and the eggs are all the same color but the innucubators are different based on the tech tree you choose.