I was not very well prepared for last night's session, but it was going to be a short session, so I had a not-thoroughly adapted pre-written side plot ready...

Short version - players did great and were creative and I loved what happened because of it including going off-course, but between events and rolls they now have a yellow Faerie Dragon, her molting (or whatever scaled animals do to change skin) mate who is in recovery from the attack before the players arrived, and two eggs traveling with them.

I think I can play the Faerie Dragons. I don't plan to have them actively engage in battle if possible or to be seen by strangers and their primary goals would be safety, new territory, and hatching their eggs. I'll leave it open with PC interactions with them if they stay a longer or shorter time or indefinitely. (That seems like a decent outline, right?) But I don't know how to handle the eggs? Would they hatch a special way or only in certain conditions? Bond with what they first see? Screech for hours as a nod to newborn humans? I want some flavor and realism and my questions are all I have today.

As a new DM I feel like I roll with twists okay in session, but once I sit for a minute the next day going over my notes and vague outline for next session I start thinking, oooookaaaay, now how am I supposed to make this "realistic" aaaaand fun?

I'm actively trying to push myself out of my comfort zone to not detail plan everything (I'm a details person by default) - just vague this mountain with cave systems is here, active quest directions/hints/rumors lead this way, random encounter tables, adapt some side quests, make up whatever isn't planned... and it's stressful but I think it's in the right way. The players are feeling out their freedom and consequences (and their feedback is a surprised approval at how the game is going, but they all know this is me learning) and I am learning to adapt and improvise. Any advice on how to continue to improve that? We are playing with a strong focus on role playing, character development, and plot advancement. I want to make sure I "level up" with my characters. I'm trying to condition myself for the lazy DM style of play because this group is interested in a long-term campaign and I don't want to fizzle out emotionally because I over stressed and I'd rather learn to roll with their choices than spend all my time planning next session. Tips and tricks?

google "bonding with loiosh" then read it.

Is it The Book of Jhereg? Khaavren Romances? Vlad Taltos books? Or Brokedown Palace?

I hate spoilers so I habitually don't read book descriptions. Google popped up all of these and they all look good, but to which were you referring? I love book recommendations btw so extra thanks!

Sorry, Book of Jhereg. Just read the whole thing, you will not be disappointed.

To avoid potential spoilers, I'll say this: in a few adventure books, it lists the hatching conditions of a species of dragon. It included things like temperature and humidity. And in one it mentions that a hatchling would bond with the first creature it sees.

It didn't mention fairy dragons though, so if you want them to be different, up to you.

Oh man, no joke. I've been burning through them. Thanks for the recommendation! 

Thanks! I feel much better equipped to handle this now!