Will the order in which I try things be critically important? e.g., can AussieSusan's HP1000 extension be tried independently from your weewx_interceptor driver?
you can try things in any order. in fact, since communication is via a network interface, you could even run multiple instances of weewx at the same time to communicate with a single station. however, there can be only one driver active for each instance of weewx.
https://github.com/weewx/weewx/wiki/Change-driverhttps://github.com/weewx/weewx/wiki/weewx-multihaving said that, i HIGHLY recommend that you keep things simple until you understand what is happening. make sure you can walk before you run

install weewx and choose simulator
then install susan's HP1000 driver and try that. if it works, yay! if not, look at the log file, and possibly post to the weewx-user group for help.
still no joy? then install the weewx-interceptor driver.
the interceptor is more complicated because it requires some network configuration that is not part of weewx. it is not hard, many people have done it, and there are some recipes that show what to do, but it is not a one-click solution.
here is one user's process for installing the interceptor driver:
https://github.com/weewx/weewx/wiki/hostapd-WiFi-setup-for-Interceptor-driverthe interceptor readme is more of a reference and assumes that you know how to make the configurations happen, but you might find it useful:
https://github.com/matthewwall/weewx-interceptorm