Awful lot of fish for a new setup. I would keep a close eye on your water params. especially with the rays being susceptible to nitrites and ammonia. They also might start picking at the rays and stress them.
As for as the size they reach around 14" or so in captivity. I have two Lents from the Orinoco that are 11' right now. 3 years old. By the way if you turn out to have Orinoco variant and have an extra female I would definitely be in the market.
You can see mine and nibwrench on page 25 of the pike photo thread.