Ah, you also changed the counter reset, that is making more sense now.
To simplify the schematic more, use an ULN2003 for the LED's

Most starterboxes are powered with 2 simple 540 motors in series powered by a 12v PB battery, 12S NiMh (2x stickpack) or most common today: a 4S LiPo. The Hudy starterbox is powered with one 775 motor.

I think a single 540 size brushless 13.5t or 17.5t has enough power to start engines from a 2S or 3S battery. You do not need sensors so a 3650 or 3660 with a 2500Kv rating will also be enough. I have 2x 23 turns brushed in my starterbox, These are motors I had from some stock racing back in the days.

I think 2 brushless motors which are by belts mechanically hard connected will be difficult to synchronize?

On Ali you can find several of these PCB's 75W 200W DC Borstelloze Motor Drive Control Board 6V-24V High Power Borstelloze Optische Drive Harde Schijf Fan Motor Snelheidsregelaar - AliExpress