These aren't naive questions at all, these are things I've only found out about in the last few weeks myself! (Or, at least, if they're naive questions, I too am naive so you are in ... good (?) company). I'm pretty sure you're better at a lot of this than I am, having seen your 68net project, so...
Do you really need the PIC there ? I know a lot of code and work has been put in developing a transceiver for that chip but how much would it cost to port that code to the esp ? (Maybe that's too much)
The problem here is that LocalTalk timing is
really tight. The throughput isn't much, but the timing and latency requirements are actually pretty stringent. The ESP32 is running FreeRTOS and has quite a few concurrent tasks flying about to do things like background housekeeping of the WiFi and IP stack, etc. While I haven't tried it personally, people who have tried similar things have told me that getting that kind of timing guarantee out of the ESP32 is very difficult going on impossible, because of the other stuff going on.
So what it boils down to is "The ESP isn't well-suited for the job, and people who are much better at this than I am have found the job difficult, so I'd be doomed". That, compared with how neat and easy and all-around pleasant the TashTalk is to interface with rather made that decision for me. The PIC is a reasonably low-cost part anyway.
I have a really old experience with PIC, and back in the days you needed a 12V power rail to flash them. Is it still the case with the PIC you are using ? Do they have a bootloader ? If it's the case flashing them from the esp would be a cool option (but I think I'm being too optimistic here).
You do need a special voltage to flash them, yup: and I'm pretty sure there isn't room in there for a bootloader. I'm socketing the PIC in case someone finds a major bug in the TashTalk firmware: and in that case, we will all swear and I will have to send people replacement PICs, and we will, in the euphemistic argot,
have learned a valuable lesson about patching.
It'd be lovely if the ESP32 just set the PIC up and we could just drop a blank PIC in but unfortunately I think that'd add as much complexity as the entirety of the rest of the circuit.