Which SaaS boilerplate features should I seek in my project?

It totally depends on your product and preferred tech stack. But most of the big ones will likely have very common feature sets so there's not that much differentiate on.

One thing I'll mention is configurability. Most boilerplates ship with tons of stuff - some of which you won't need. This can lead to having a lot of unused code lying around which can be a maintenance burden long term (or you have to do a bunch of work to safely delete it). A handful will let you build without certain features enabled which makes the starting codebase more tailored to exactly what your project needs.

What are you building? What features will you need?