I assume that when you say:
If a player uses an ability that allows a player to use a Second Wind, you can heal HP for free without spending your Second Wind encounter power. Same as above.
you mean "spend a healing surge" instead of just "use your second wind." So, for example, a Warlord's Inspiring Word (at 1st-5th level) would heal for (1d20 + target's Endurance) + 1d6 (for the bonus from Inspiring Word). Is this correct?
Also:
This would make it 1d20 + Lvl/2 + ConMod. Or, more like
2nd = 12+
6th = 14+
10th = 16+
And so on, adding 2 every 4 levels. So, it's initially a lot more healing from a second wind / Heal but it's later a lot less. I'd suggest trying to coax that scale a little closer.
This is not accurate because it ignores benefits from skill training or skill focus. I would venture to guess that most, if not all, characters would train Endurance - 5 additional HP from every heal is a lot, especially since most healing only functions in combat. (Just for clarification: Are there ANY healing powers other than your new Bind Wounds that function outside of combat?)
Anyway, as for the effects on balance:
First of all, it makes Leaders a LOT more useful. Since the players have very limited healing outside of combat, they can only sustain their adventuring if the number of HP they can heal during combat is at least as much as the number of HP they take in damage every combat. Thus players will have to load up on healing powers if they want to survive. And since there are no more healing surges, there's no limit to the amount that can be healed per day.
As an aside, the intended purpose of the existing healing surge system (as I see it) is to balance out the power of leaders and other healers. The HS system makes it so that a party without leaders or with few leaders can still survive, because players can self-heal after combat. Nevertheless leaders are still very useful, because they can heal others in combat, which is otherwise hard to do. But a party can't just load up on leaders and be nearly invincible by pumping out as much healing as possible, because they'll quickly run out of healing surge.
Your system gets rid of the "boost" on the low-leader side of the comparison, which seems to be what you want - to make the game more dangerous such that leaders are required to survive. But you also seem to remove the effective "healing limit," encouraging a party to load up on as many leaders as possible. One option to consider might be keeping healing surges as a limit on the number of times a character can receive healing, but remove the "self-heal to full during short rest" ability if that's what you want.
Also, the mechanism of healing powers only working during combat encounters seems to encourage two possibly unwanted behaviors: (1) keeping one monster alive until everyone's used up all their encounter heals and (2) intentionally seeking out weak encounters in order to use the healing. For example, suppose that players were fighting a bunch of kobolds. They could capture one, and then if later in the adventure they were running low on hit points, they could release the kobold and fight him, starting a combat encounter. Then they could go through a whole another cycle of encounter healing, and whack the kobold one more time to finish the job. (And they could even due this multiple times with the same kobold!)
Of course, (1) could be dealt with by allowing players to use all remaining encounter healing immediately after the end of a combat encounter (but after that they can't use it again until the next combat encounter), and (2) could be dealt with by not recharging players' healing after very weak encounters (kind of like how the DMG says you can discount weak encounters when calculating milestones.)
