My retirement project is going to be this but at larger scale.

Remove the tires from two old bicycles to run them on rails, build a gantry between them mounted to seatposts and handlebars. Probably drive it with chains on winches for robustness.

Use movable wall elements so that the pick and place machine can set up both shade and increased illumination. Maybe have portable rain protection too. Maybe deploy close-up UV and IR lamps.

I'd like to know the max size that a single gantry can serve, see how high its utilization can be.

My guess is that it all can pay off once it's big enough. I just don't know where that point is. 100ft long? 200ft? 300? And 20ft wide?