Considering Show Canon
The first stories were set shortly after the end of season 2. All major events--Twilight's ascension, Tirek's rampage, Thorax's transformation--are fair game for exploration. Prequels set before the Battle of Canterlot would also be welcome.

Changeling Society

Changeling society has one rule above all others: loyalty to the Hive. And no one represents the Hive more than the Queen Changeling herself. She is born different from the drones, born with irises and pupils in her eyes that mark her as the next leader. She learns the ways of the Hive from the current Queen, and when she ascends, her will becomes law. Opposition is not tolerated. Food and love are too scarce in the badlands to support warring factions.

Thus, drones understand their place in the world. They live and work and serve to ensure that the Hive survives another day. Nothing else matters. They call each other Brother and Sister, for only the Queen is worthy of being a true individual. She's the one that is different, after all. She's the one that has been set aside her entire life to rule over them.

When the Queen fails as spectacularly as Chrysalis did against Canterlot, and when the Hive fails by extension, all bets are off. What has that loyalty earned the drones?

Love and Food

Seeing as changeling can do everything other animals can do, they naturally need the energy to run, fly, fight, whatever situation comes up.

Love is a changeling's top choice when they can get it. Love not only can sustain them, but it can power them. It makes them stronger, their magic more powerful. They can sense it and feel where the love is coming from, and where it's directed. When love is directed at them--at the form they're shifted into or themselves directly--they can feed on it freely. A changeling could also magically draw the love out of someone directly, but this method is risky, not to mention frowned upon in pony society. If the target is strong-willed enough, it can be resisted. It's also overt and taxing to perform. Not a viable strategy when surrounded or being chased away.

When love isn't an option, a changeling can also draw on regular food and water. This has none of the extra benefits of tapping into love, but it can keep them going long enough to find some. They also have no reservation about using their fangs for hunting if they need to.

Changeling/Pony Relations

Twilight Sparkle was the first pony to befriend a stranded changeling after the Battle of Canterlot. He took the form on a bit of printed ink in her books to hide from Spike, much to her surprise. They quickly discovered the benefits of this idea, that a pony enraptured by the book they were reading would freely donate their love to a changeling hidden within while being none the wiser.

This changeling took the name Stormy Night, and over time, he recruited more and more changelings to come join him at the library and fill themselves to their heart's content. Twilight welcomed the opportunity to learn more about this new species and see if she couldn't bridge the tension between their peoples somehow.

Her hand was forced when the changelings grew restless from staying in books all day and were discovered soon after. Summoned before Princess Celestia to explain herself, Twilight made her case that changelings and ponies had the potential to live in harmony together. Celestia agreed to give the changelings a chance, but held Twilight's methods reckless without supervision.

The Princess decreed that any changeling that wished to live in peace within Equestria should reveal themselves to a local mayor or guard station. They were not to be harmed or imprisoned, but taught Equestrian laws and customs over the course of their day-to-day lives. If a town or city did not have the resources to monitor all the changelings seeking asylum there, the extra changelings were to be escorted to Canterlot.

Where Things Stand

Ten changelings are peacefully living in Equestria. Six of them are under Celestia's watchful eye in Canterlot, and the rest settled in Ponyville to find work and get accustomed to Equestrian life.

News of the changelings' presence is filtering slowly through the rest of the country, along with Celestia's decree. Ponies may be suspicious or frightened of their unexpected neighbors--and defend themselves if threatened--but they trust Celestia's judgment. A royal order is not ignored lightly.

It remains to be seen exactly how many changeling were scattered from Canterlot, where they have wandered to before hearing the news, or how many may be willing to trust the ponies.

5892375 Primer indeed!

This is a really helpful start, having the gist of the trilogy summed up so nicely. I have an idea or two for stories in this 'verse, but I need to set my priorities before I put them to paper.

5895739
I did three one-shots in about two years, so time is definitely on your side.

5895750 Well, unless somebody pinches my idea before I get it down first. Otherwise I'd look like a copycat.