For a project as thick as this there are firing considerations. You probably want a rate of advance no more than 50C/hr to 250C, 70C/hr to 540C, 100C/hr to 630C, 120C/hr to top temperature (possibly 740C) with a 10min soak. The annealing cool needs about 6 hours at ca. 540C, followed by 7C/hr for the first 55C and then 12C/hr to 110C below the annealing soak. Then a cool of 40/hr to room temperature. This is a two or three day firing.
Texture can be achieved with fibre paper scrunched up, or sand with aluminia hydrate powder on top of the sand to keep it from sticking to the glass. Tin side down will also help keep the sand from sticking. This is transparent not opaque, which a sandblaster would introduce.
Dams will be required, unless you are prepared to watch the firing. If you watch the firing, you will be able to stop the firing just as the top edge rounds and before it begins to flow. This will avoid the need for dams, and the subsequent cold working required. But note you will see the layers of glass on the edges. It will not appear to be a single slab.
This is something that you will need to experiment with for a while to get it right. It is very thick and heavy, so you may need help to place the glass in the kiln and to remove it when it is a single slab three times heavier than each piece you put into the kiln.
The thickness you are proposing will pass almost all existing strength and safety standards. Normally 19mm and thicker glass does not require toughening. The safety concerns are about it falling onto someone, rather than breaking.