If you want short ropes, you can also just go to a climbing store and buy per feet of the rolls they have.

9.9mm is not light nor thin for a single rope. The thinnest single rope rates ropes are 8.7mm. (ofcorse with reduced durability and lower friction in belay devices).

If you use rope with belay devices and carabiners, try to keep the rope clean. Dirty rope wear down equipment fast. Impregnated rope help with keeping rope clean (and drier = lighter).