I don't see any problem with this from a mechanical perspective. In effect you're just using a custom race for your PC with a significant amount of flavor elements. I would model it on an existing race (probably the race of your druid), and modify the flavor rather than the mechanics (or maybe one racial feature). It's appealing that this is mechanically one PC, and not you playing 2 when everyone else is playing 1 (playing 2 PCs without a specific commission to do so from your group can be problematic)

However, this is a concept that will take a lot of work for both you the player, and also the DM to support, make sure you talk to him (and the other players probably) and that it will be a good fit for the game that you are collectively playing.

One of the important things, I think, is to design this guy to be a functional PC. No one likes a party mate who doesn't pull their weight, especially when he's got a complicated back story that might be difficult to role-play with.

So if you have a race to model your PC after, have DM and player buy in, and build him to be a reasonably effective PC, I see no problem with it mechanically or at the table.

The Temporary Hit Point total is equal to the "Inspired Leaders" Charisma Modifier + Level.

Therefore at first level, assuming a 15 in Charisma, they would spend 10 minutes listening to the Inspired Leaders speech for 3 Temporary Hit Points each for up to 6 allies.

To answer your question, yes it is a hit point boost to the party that increases as the character with the feat levels up, and improves their Charisma score modifier.

The only reason they should not be able to take advantage of it after every short rest is if they do not have the 10 minutes to listen to the speech or if giving the speech would attract unwanted attention.