These are best bought in packs of 4 units and 48watt will be very bright for the average height garage. The mounting kit is not worth using in a garage so any of the shown fixings are good enough. I used small pieces of plastic strip used for plastic window edging. There is no complicated wiring and no earthing to worry about. All ebay suppliers are using similar units so look at the feedback to see if they are good suppliers and buy the lowest priced items.
Easy to buy more if you need more light. There are 60 watt units now but they are better if ceiling height is about 9 foot or more.
Next time, i might tell you about microwave energy light switching as the units are now only 11 pounds. As long as you are moving just a tiny amount, the light will stay on and switch off just after you leave.These units will allow detection through glass so quite good as a burglar deterrent,lights will come on as you pass the window of the garage.They will also detect a little tap with a finger on a garage door.Extremely sensitive.