Nice garage. Be very careful about drilling into the reinforcing rods, you can easily crack the concrete. Even a hairline crack will allow moisture in and will cause spalling (flaking of the concrete due to the rod rusting) and cutting through a rod could impact on the integrity of the panel.

Have you considered how to heat it in winter? The thermal conductivity of those concrete slabs is suprisingly high, it will be chilly in there in the winter, even with the OSB acting as sone insulation you'll need approx 4kW to maintain an internal temp of 20degC when its 0degC outside. Personally I would have glued 50mm battens to the concrete at suitable intervals, filled the gaps with 50mm insulation and then screwed the OSB to the battens. Would be quicker to install, and warmer.

What are you planning to do about the roof? Apart from the obvious gaps you can see due to the corrugations its also a major source of heat loss and needs at least 75mm insulation. Ditto the door.

I like the floor mats, but sadly I thnk they'll look very grubby soon. Are they washable?