So my question is, would you guys like to see a few heroes who are very customizable, or lots who aren't? How many heroes and skills should, in your opinion, become the standard for the genre?
The number of heroes should mainly depend on the size of the map, yet other variables such as custom made maps and number of opponents may also adjust the number. A small map with 3 heroes would be normal. On the 64bit map sizes for Elemental which may use 4GBs of memory from a system with 6GBs I could totally understand having a hundred heroes or more.
How many skills... this is more subjective, but if done correctly the number of skills can be near a hundred. If it's not done correctly than lots of skills can cause game balance issues, longer learning curve, decreased game stability and possible other side effects.