No worries!
When I want a character do an animation directly after another animation, I use is for the first animation and then starts for the second animation.
I know their purposes can sometimes come off as confusing, but I hope you can remember that (if you want to) for whenever you need an animation to happen directly after another. The format has always worked for me and should for you too. 
“Is” is mainly for allowing characters to play through full animations and “starts” is a more cut-in command that doesn’t focus on full play through hence why it doesn’t have those idle pauses when it comes to animations.
I haven’t read this guide, but it might give you a better explanation of it than I can and it may perhaps help you with future scenes:
@kahlouchee I love the effort you’ve put into helping firefly!