I, perhaps wrongly, assumed that I could configure the PIC16F88 for three analog inputs. I want to read AN0, AN1, and AN3, not necessarily at the same time, i.e. useconds are not critical. So, since it appears from the header that I can only configure for one ADC at a time, do I have to call a version of these statements every time I want a different channel?:
All PICs (that I know of) only have one actual ADC. You have to select the channel you want, do the conversion, select another channel, do another conversion etc.
Switching channels takes practically no time at all compared to the ADC conversion time.
I don't know what exactly those function calls do, but it sounds like set_adc_channel is all you need.