Does the increase of healing from Heart of the Wild, Incarnation: Tree of Life and the legendary ring stack giving a total (temporary) increase in healing by 65%?
If you popped both those CDs and the ring at the same time, then yes:
25%+15%+25% (base level ring) = 65% increase.
Rarely will you need that much of an increase at once since you'll be doing a lot of ineffective overhealing - (usually - not always but usually - its better to spread CD's out - with the obvious caveat of its more important to use them based on the damage pattern of a given fight and its mechanics.)
But if you really need to blow your wad for whatever reason - yeah they all stack
If you're thinking about making a big shield, it doesn't work. The game actually recognizes that you're overhealing, while logs don't. If you're thinking about ranks, go for it!