I'd like to see 51 at launch with the power to vote to expand that number as the network grows. The way it works is, Bitcoin uses delegated representation with mining pools, but if the pools do something bad, it has quick fault recovery. DPoS can be more decentralized in that regard, having a much larger number of"pools", but it has worse fault recovery. Due to this dynamic, the DPoS system obviously can't utilize a similar number of block validators as Bitcoin, it needs to be greater since fault recovery is worse. Anything below 51 is also bad for collusion.
I was going to wait till after launch to run for delegate but can probably get up to speed on running one beforehand.