Don't have a cow, it will be easy. :)
Ideally it should be easy to learn, difficult to master. We'll have a basic set of genes that would allow bots not to care to much about metabolism, except for the fact that there energy can be converted to stuff with different properties, like fat, carb, protein, muscle, shell, slime, venom, poison, lignen, chitin and so on...
These will be copy-paste genes/enzyme sets. You just decide: In my bot I want to have muscle and venom, then choose the set and copy/paste the stuff at the end of your genome.
if you want to get fancy - evolve stuff or dig in and learn.
Would that work for you?