"transceiver" is just the term for the driver chip, i only use in one direction
there is an extension of the protocol that allows for a response from the light, i don't know how widely used that is or how much data traffic would be involved typically, my wild guess is little

so i don't plan to support bi-directional and am aware it would be somewhere between challenging and impossible to do well
nonetheless if the pins are available as an architectural thing i plan to allow movement in that direction in the future if it does not complicate the hardware overly

re the the benefit of a 5V PIC, i am sure i could use a 3.3v part and a 5V transceiver (driver) chip and that they could play nice together but now the power system is maybe a bit more complicated

initially i planned to let EVERYTHING run on LiPo voltage ranges 3.0- 4.2V
the pots are ratiometric on the A/D, so that works fine
but i have been advised not to run the RS-485 at 3..3V as it is not best practice
do then i would need a DCDC converter for the driver chip
with a 5V PIC i now have less different voltages to distribute, but i guess there will be a converter either way as i think about it (boost from LiPo to 5V)

still 5V simplifies life as the wall wart can be 5V and override the LiPo
getting a slick instant change over battery is going to be a challenge in itself, down time to charge is not acceptable, mechanically i would much rather have a buried one

yeah, i realize 1% is 1% whatever the rate what really meant was whether 1% is good enough for professional comms ?
googling around just now it seems that actually +-2% should be ok

there is one more fly in this soup ...
there may be i2c transmissions that need to be squeezed in somewhere, maybe 5 - 12 bytes worth (could be broken in half into two bursts)