1. depends on if you need to build custom modules/plugins. Alot of the functionality that you seem to need can be created using already created modules(plus my experience is that if I'm thinking I need to build a module one is already out there.)
2. I've heard they are trying to make this better, but it can be wonky. A lot of times developers will wait 3-4 months to allow modules to catch up to the new version.
Another option may be Backdrop (backdropcms.org). Which is working on maintaining backwards compatibility.