Much like Willow maybe there's a lot of kink beneath [Kaylee's] sweet and innocent exterior?
Oh you've nooooo idea.
Re the guns:
I think looking at the 21st century pop-guns and trying to gleam something from them about what they represent as 24th century guns is... stretching things. Esp. saying the guns the props represent are the same make and model of gun in this setting is... silly. They're futuristic guns that simply look
like their 20th/21st century counterparts. Heck the guns even make electric whirs when cocked and fired.
It seems like you more-or-less got a decent bead on the series but as Mal said, somewhat harshly, you need to not look at this like the teen angst of the Buffy series and look at all of these characters as adults in a very mundane universe. Keep with the series all of the episodes are good episodes, there's only one I think is weak, and the best ones come on, IIRC, Disc 3 (notably "Out of Gas" and "Ariel.")
Seriously, if after watching those two episodes you don't think this could've been a really great series then I don't think there's any hope in the 'verse for you.
Only seen Serenity so far so I can't say but I'll try to get The Train Job done this weekend. As for the sexual aspect well that depends on the ep itself, it they're all as steamy as Inarra in the first ep, no promises