All good questions.
The setting is essentially original, though based on elements of campaigns published or implied in modules.
It's a pseudo-feudalistic setup, based upon a kingdom with its assorted Duchies, Baronies, Counties, etc. The "enough of a railroad to get everyone together" if you will is based on the idea of increased raids along the Marches of the kingdom, whether from the King himself or from his various allies .. to account for Elves, Dwarves, Gnomes, and of course humans that are not from the central Kingdom.
Again, the push of the campaign has to do with humanoid and bandit raids and attacks. The kingdom has become somewhat ineffective militarily, and to compensate the adventurers (in the main party and others) are commissioned as Royal Agents to go in and see what can be done.
Happy to answer other questions if that doesn't answer any given questions anyone has.
Starting level is level 1 regardless, beginning with suitable low-level adventures and ramping up as characters gain experience. Character creation is going to depend on the system, but most likely will be 4d6, drop lowest, in published ability order (dependent on edition, since there are some differences). Regardless of system initial hit points will be maximum for the character at first level, and standard rolls thereafter. I will likely use training rules in any case, so level increases are dependent upon both having the experience points, gold to train, and availability of a trainer.
As I said before, characters will be 'railroaded' into initial position, then from that starting-point are free to go where they will. Noting, the expectation of the Royal Court to 'make some kind of difference' on the Marches.
Going beyond this point, I am wanting good roleplay, since this is Elliquiy. I'd like fairly developed characters, with of course the pride in advancement, sorrow in loss, that would go along with it. Adult content isn't the focus, but I'd probably place it in NC-E to be safe. Y'all know how Orcs are after all *heh*