Integrating CAN bus into older vehicles

Hello friends, I've noticed that some of you have experience with CAN bus and the environment it requires...

My plan is to connect the R36 engine with a suitable engine control unit (ECU) and a DRP gearbox, while also being able to use the R36 speedometer without needing the new ABS system, but still utilize the complete FIS (multifunction display).

The R36 runs in my 2-series without WFS (Wastegate Function System) or similar add-ons...
Do I need any additional control units or a special ignition switch to be able to use it like this?

I'll need a CAN bus converter to convert the speed signal from the analog transmission sensor into CAN signals, which will then be used by the speedometer and the transmission.

It would be great if some of you could contribute something to help me move this project forward.