You will need to do some research on what size tank you can make out of glass as thick as yours. I would hesitate to spend money on this project since the appeal to me would be to get a tank for free or near free. I do not know if you will be able to make a tank 48" long out of this glass. You may need to go shorter.
Regarding the lid. You can get tabs that let you use glass as your lid. Basically it would sit even with the top of the aquarium.
If open top is not an option you could cut it down shorter and use the glass you cut down to create euro bracing. That way you could make a 48" tank. Again you will want to research how big a tank you can make using that method to make sure you don't have a busted tank.