Questions about converting an old pointing device to USB

I found an old Kensington trackball at a yard sale, and I thought converting it to USB would make a good first arduino project. If that works, I’m going to convert some old Kinesis keyboards I have to USB. I am quite inexperienced at playing with hardware, so I welcome any feedback on the feasibility of these ideas as first projects. (Of course, the point is to get some experience, so I don’t really care if it would be more cost-effective in terms of time or money to buy new peripherals, but I would love to know if these projects are going to be hard or frustrating for a beginner for some reason I haven’t forseen.)

My plan is to wire the sensor components in the trackball up to an R3 arduino, write a small program to report the readouts from the sensors, then program a SparkFun ProMicro to provide USB output, as outlined in part 2 of this page.

The trackball has an old Mac serial output jack, and I don’t really know how to connect it. I am thus unsure about how to determine the voltages/power levels its sensor components require, and slightly worried about frying them. Is there a way I can program an arduino to control the power it provides to a component, or should I include a potentiometer in the circuit I use to explore their outputs?

In case it clarifies anything, here’s a photo of the trackball’s PCB.

Wow, that's pretty impressive for a first project. I think my first project was blinking a few LEDs.