- I've read that Volto and the restapi package will work with an existing Plone 5 site – are the advantages to upgrading to Plone 6 before doing the frontend migration?
The advantage is that you can use stable and well-tested components today. Plone 5.2 is battle proved, same as Plone RESTAPI and Volto. The upgrade from Plone 5.2 to Plone 6 should be trivial, there is only the siteroot PLIP that will make a difference and require a newer Volto version in the future. You can have the full stack of Plone 6 today if you want. There is no good reason to wait IMHO. Though, I am biased here of course.
- How important is it to adopt Blocks? (I believe the site I'm working on only allows users to modify schema-based content, I don't think there would be much use of the Pastanaga Editor)
Volto will work fine without the blocks behavior. Though, you will miss most of the killer features of Plone 6 / Volto, they are all blocks based (listing block, search block, tons of add-on blocks, etc).
- I've seen the RedTurtle migration packages but I'm finding it difficult to understand how they work and I can't find the original talk where they were discussed – anyone know more about this?
We have a full migration pipeline at kitconcept that we used for multiple larger client projects already. Problem is that larger migrations tend to be complex and our code is full of client-specific customizations. This makes it hard to open source this as a whole. Though, we provided redturtle with the core of our migration algorithm and they open-sourced it. If you know transmogrifier you should be able to write your own migration with that information. Though, we are aware that this is far from perfect. We plan to get together and improve the migration situation to make it easy to migrate from Plone Classic to Volto / Plone 6.
- Is there anyone out there who has migrated from Classic to Volto and written about the steps they took / pitfalls they uncovered?
As said, we did this for lots of projects already. RedTurtle and possibly others as well. The Plone conference will be a good place to start a discussion about how we could help people to write their own migrations and provide a standard upgrade path to Plone 6. I guess we are looking for someone to champion the migration story and push things further...please bear with us for a while or become involved and make it happen faster.