Well it depends on exactly what you want to see happen.
Bots aren't really good at evolving new behaviors. Shot bots rarely learn to tie, etc. Instead, bots tend to get better at the whatever it is they already do. Shot bots learn to always shoot. Bots in high friction sims learn to compensate, things like that.
A population size of about 100 bots should be enough to geta good sim going. As to field size, at present it shouldn't make a huge difference, but a size of about 3 is best I think.
Half the trick is patience and the other half is being able to figure out success when you see it. Evolution has a really chaotic effect on DNA, so looking at DNA itself don't be expecting too much.