Thank you!! It's been a lot of work but the results are gratifying.
Belly sizes multiply the number of sprites needed by a lot - especially when things like weight gain is considered as another feature in the future, I really have to do what I can to rein in the excessive number of belly sizes. Currently the player has over 3,500 unique frames of animation, and each new belly size would add almost another 1,000, which will then get at least tripled when features like weight gain are added. In regards to your suggestion about weight gain, I plan to have 3 areas gain weight, with each being togglable so you can decide where gains go - breasts, belly, or butt/thighs.
Despite the sprite issues for the 1.5/2.5/etc belly sizes, there is a new enemy coming to the next update who is roughly half the size of typical enemies, and therefor can be eaten to get that "half sized" belly with squirms and all. In order to avoid the conundrum of then having to sprite sizes for 1.5, 2.5, 3.5, and so on, these enemies will still count as size 1 after the first eaten, but it will at least allow the half sized belly to see a lot more use.
The enemies you suggested are also fairly similar to ones people have suggested before, so they're likely to be added in some form or another!
For test mode, there already is a kinda "test mode" available in Patreon builds as they have access to a special level that I use for development testing, but I do also plan to add a free play level at some point similar to this to the main game for everyone to use. I think the debugger should be available in all versions though (f3 to activate), and while the debugger is active, you can access a few cheats like manually giving yourself DNA points.
If you make any fanart do please share! I love seeing fanart of the game :)