Help needed: Roller racing rig goes digital!

Anyone able to help me with a thing? I’m doing up an old roller racing rig and I want to give it a digital timing upgrade. in theory this is pretty straightforward:

1. magnets on the rollers, hall effect sensors counting revolutions
2. Arduino doing the counting and timing
3. LED displays showing the times

There’s a few other bits and bobs i’ll probably add too, like a simple sound board. anyway, fixing up the rig i’m fine with and i can program an Arduino okay, but designing and building the circuit isn’t my particular sphere of expertise. anyone out there interested in helping out?