How does experience count when high-level and low-level players are in the same party

You can check here how it got to the current FFA looting.

In the first page, you can see the official response:

When an item drops, how do you decide who gets the temporary allocation? Randomly among nearby players.

By the way, it's still an open beta, so it may change with any patch.

Rallying Cry has the property "Warcry" and is not actually a spell anymore. This means is cannot be cast from trigger spells like Cast on Damage Taken and Cast on Melee Kill. It is manual cast only and also has a global 4 second cooldown.

Totems have their own special "Totem" property as well, and also do not work with "Cast on X" support gems. They are also subject to the totem limit (1 per character by default, with some special exceptions).

Furthermore, Cast on Melee Kill must be linked to both the spell you want to cast on kill and the melee ability you are killing with. It does not create a character-wide effect like Cast on Damage Taken. This means you need at minimum a three-link with the melee skill you want to use to trigger the spells.

And finally, there is an internal cooldown as well as a spell ordering for each "Cast on X" gem your character has. This means you won't ever cast two spells at a time from the same "Cast on X" effect, and they won't cast the same skill twice in a row if there are multiple valid spells linked up. From what I remember mana is never taken into account for these spellcasts though, so they are always free (especially important to know if you take Blood Magic).

Unfortunately, this means you can't easily create a character that summons totems in rapid succession on kill, sustained by Warcrys. Generally, unless you heavily center your build around Cast on Kill, it is better to link the melee skill to something with more damage or better utility.