Replacement parts availability?
 

So, I have my new bike.
How long into the future will spare parts be available, do you think?

In particular, I'm concerned about the 11-30 cassette, the F/B derailers and the combo brake/shifter handles.

Depends. What brand/model of components are we talking about?

Shimano Acera. All of it is, I think. Not too sure, though...

Shimano still makes parts for 7 speed systems that stopped appearing on new bikes around 10 years ago. 8 speed is still going strong on Shimano's lower end groups like Acera and Sora, so I wonld not expect parts availability to be a problem for many years. BTW, the only parts that are really 8 speed-specific are the cassette and shifters. You could substitute derailleurs and cranks from 9-speed groups and they will work fine.