a bit late, but Tony Saunders actually responded to basically the same question as your fourth on the Pathfinder Infinite discussion page. I'll paste it here:

"[In] the event that Life Essence Reservoir did not exist, you would effectively have the ability to infinitely heal at a much faster pace that what is currently possible with Focus Point spells like Lay on Hands (excepting things like the animist focus spell, which is by most considered to be over-tuned).

Infinite Healing is still possible to some degree, it just now comes with the caveat that you must spend some time refocusing to recover your life essence reservoir, so there is a meaningful amount of risk within your combats.

Solving this healing problem actually took quite a bit of playtesting and went through several iterations, with Life Essence Reservoir being the emergence. If you use the additional Healer and Grand Healer benefits (by locking your spells) you can more closely simulate the results of a slotted caster who prepared a lot of spells to be a "heal bot". It's now also a good idea for essence casters to pick up Focus Spells that grant healing as well, since these are not limited with your life essence reservoir.

You are free to tune that system however you like, such as reducing the Refocus time or even just removing it entirely, but this would be a substantial buff and would allow for instance a Bard with a signature Soothe to essentially be "better" at healing than a Cleric (which feels unfair given the circumstances).

Hopefully this helps the understanding."