First, I believe you should have no problem running the Colu colored coins protocol on top of MultiChain, although it's not clear that it makes sense to do this, since you can also use MultiChain's native assets instead.
There is no minimum number of nodes technically, but in general blockchains don't provide meaningful resilience to malfunctioning or malicious behaviour unless there are at least 3 nodes.
And yes, you can configure the block times easily when creating a chain, down to 2 seconds (though see the note in the documentation relating to that):
http://www.multichain.com/developers/blockchain-parameters/