Hello. I registered with this site just to answer your questions.
1) Corn syrup may actually add to the stickiness of the overall piece. Experiment with it and without it.
2) For those in the U.K. you may have a lot of trouble finding corn syrup. Use Liquid Glucose (about 79p from tesco baking aisle).
3) Add food colouring AFTER you have made the sugar solution. Adding it before will simply cause it to evaporate with the water.
4) YES, YOU DO NEED TO STIR IT. The sugar needs to dissolve into the water, achieved by stirring. The same goes for corn syrup or liquid glucose, if you are using it. To make brown sugar glass, simply burn the solution.
5) You can use Isomelt instead of sugar, but you may find this to be a lot more expensive than it needs to be, espcially if this is your first time making sugar glass.
6) Plain sugar glass IS clear if you have made it right. The solution will go from cloudy to clear it heats up. Images will appear warped through IT, but is IS clear.
Making the sugar glass is easy. Moulding it is the hard part.
I am currently working in SFX for a regional television channel in England - none of this is guesswork.