The most important thing is the amount of energy going in and out of the field, which is turn related to how good your bot is at feeding and burning up its energy. The only thing I can suggest is to experiment with the bot your going to use and try and get a good balance. You want to try and make the enviroment as harsh as possible while still letting your bots survive. Apply some common sense to your sets, veg constantly being repopulated obviously needs more energy, veg constantly maxed out needs less.
I'd suggest using KE mode or possibly Zero Momentum (havnt tried that at length yet, might fun). As large a field size as you run at a reasonably speed. Around ~5 nrg for vegs though adjust it to suit. Also the mutation rates as slow as you can stand, the higher numbers the better chance of bad mutations being killed off leaving decent ones, I use around 25,000 to 50,000.