I saw this invite very late. Thanks for inviting me to take part in this discussion.
I am biased and don't like the SaaS idea very much. I like, the newly created term Feature as a Service (FaaS) by algolia.com, much more. Because now it's up on me or us to pick the features we need and combine them to anything great.
Typical SaaS solutions tend to allow only changing brands. That's why I tell to now build SaaS solutions neither by picking boilerplates or generators or going from scratch.
If the decision is unmovable I would go from scratch. Pick a backend language, pick data storage(s), build API in the backend talking to the storages. Now pick a frontend language collection and build the UI and connect it to the API. Multiply the backend and stress test it to see if it scales, adjust accordingly and go live.