Controlling multiple led displays 'remotely', arduino to arduino comms methods

I'm Working on a steering wheel display for my track car. I've come to the conclusion that to provide flexibility and future expansion I want an arduino mounted to the car car doing all the hardwork (speed sensing etc) then some form of communication to an arduino on the steering wheel. The arduino on the steering wheel takes a data packet (8bytes) and updates the displays (5Hz). The connection can be hardwired if necessary (could be hard wired through the slip ring from car to wheel, but I understand this could be noisy).

I have 7 buttons on the wheel that need to communicate with the master arduino, these could be hardwired but the slip ring has a limitted amount of connections, if the connection to the wheel can have a minimal number of connections then it makes a neater solution.

Curious on your thoughts for an ideal, robust protocol and hardware solution.

Three slip rings.

Ground - of course - 12V and a data ring. Use a switchmode regulator in the wheel to convert to 5V; the converter contains capacitors and gives leeway for some intermittent contact. An incandescent bulb in series with the feed to this slip ring from 12V provides protection from short circuit.

Now for the data. A current source (say, 20 mA) feeds 12V to it on the chassis side. At each side of the interface, a 2k7 resistor goes to an Arduino input, whilst an NPN transistor can pull the interface down when switched by an Arduino output (10k resistor to the base).

You use a (serial) packet protocol - each packet in one direction or the other contains a "sync" character, a byte count, control and data bytes, and a checksum. Your software uses collision detection - if what is read from the interface does not match what is supposed to be being sent, it aborts, waits and re-tries. If an important packet is not acknowledged, it is sent again until it is acknowledged. Verifying the checksum means that interference will slow but not prevent communication.

There are libraries for much of this, generally relating to RF communication, only lacking the collision detection.