Testing it now, yeah it looks like there's an issue with Tiny singular maps. If you use binary sector, then you'll get at least one AI to show up in the other sector. The other two AIs are no where to be found though. If you want a single sector you'll have to use a small one, which should at least spawn one AI opponent.
I've reported it to the devs. Thx a lot for the report!
As for the phenotype, if you create a custom civilization, and click Choose Species (in the middle), you should be able to create a new species (button right button), there you can change the phenotype if you have the DLC.
If you are playing the game on Steam, this DLC and others can be found on the steam GC4 store page. If you plan on getting them all, the Expansion Pass would be a good option. Might want to wait tomorrow though, since I think the annual Steam Christmas sale is about to happen; I do not know if some of the GC4 DLC will be discounted, but it's still a good idea to wait one day in case they are. 