I do have a specific question for you: where do I get started on writing a script that takes button presses and generates chdkptp commands?
First, you need to figure what kind of input your remote generates: keyboard key presses, mouse emulation, or something else.
Then you have to write a program reads that input, and does something in response to it. Sorry this is vague, but it depends on how you are getting the input and what language you are using. Normally in linux, keyboard and mouse input are filtered through a terminal or GUI session, so getting the input in an easy to use form may be tricky. But again, a lot of people using raspberry pi have dealt with this, so google will be your friend.
Once you have that working, make the "do something in response" be either executing chdkptp with a specific commend, like
chdkptp.sh -c -e "=click('zoom_in')"
or write output that is piped into chdkptp, so for example you start your program like
remote_program | chdkptp.sh
and then when your program sees the zoom button, it outputs something like
=click('zoom_in')
Would this have to be a Lua script?
No, any language that can either write to standard output or execute other programs would be fine. If whatever your remote generates is easily read from Lua in chdkptp, that could save you writing separate program and add some flexibility, but the non-GUI can normally only read line oriented input from stdin. (The GUI can get key and mouse events using regular IUP code
http://webserver2.tecgraf.puc-rio.br/iup/)
Actually controlling the camera requires you send Lua code from chdkptp, like using the = command as in the examples above.
