I'm sure this has been stated, but bringing it up anyway, just in case. Talking your way out of a combat or situation, should award xp. In pnp, the dm will usually award xp for "resolving the encounter". This can be through killing the enemy, or just getting them to go away, or your party leaving the area without aggravating the situation. Now, running away, from combat, no. But if you talk your way out of it, either through good rolls, or dialog choices, then you should receive the full xp for that encounter. Hell, when I dm, I specifically throw in encounters that the PC's can't win through combat, and I will still reward xp, if they are able to resolve the situation without fighting and clever thinking.
This should definitely be a thing. Killing everything is often the easy way out, being creative should always be rewarded.
To avoid overleveling they could make it where whatever you do in the first encounter with something awards the xp and the majority of xp should be earned through quests and overall encounters.
I have played a couple games that would give you XP rewards for eluding enemies usually capped at half the XP you would earn from killing them that was subtracted from the XP you would receive from killing them. Lionheart did this and it worked really well. The XP rewarded would vary according to the distance the player was from the enemies, and as that happened the chances of them spotting the player also increased -if I am remembering correctly, it has been years since I played that title. Most games don't bother with that sort of thing, the reward of stealth is usually being able to see what sort of fight you are in for and being able to prepare accordingly which is fine as that can lead to drastically reducing the difficulty of many encounters in and of itself
Not really a fan of this. Stealth xp should be equal to regular xp, there is usually more tactical thinking that goes along with it rather than just rushing in. Punishing people for using their brains is pretty bad. Was there ranged and melee damage too? This would be even worse, a stealthy ranged player would never level.