You definitely want to sand the glass for mechanical adhesion, just not so hard or for the reason why B'ham stated.
As far as sanding and coats of finish, the best thing you can do , unless you are well versed in the level of finish you like, is to do a control sample. Take scraps of riser wood and glass and go thru the steps. Finishing is much easier if you know what to expect from your materials. That vinyl sealer is correct. Rattle cans always take more coats than uncanned , just because it has to be thinned so much to atomize out of the can. Something to keep in mind.
Assuming you are good to go, I would sand to desired smoothness, hit it with sealer, sand it down flat, hit it again if you have any low spots, sand flat and then top coat. I would not go more than two, 2K top coats and yes, knock it down between coats. I don't use steel wool, but if I did it would only be stainless wool. I just use non-stearated sandpaper. And the most important step........ Rubbing out the finish. I don't think it's possible to get a perfect, immaculate finish off the tip of a gun and certainly not a rattle can. Is it necessary?, no. Is it hard to do?, no.
Does it look awesome? YES If you you decide to rub out the finish, be sure to get gloss spray. Then you can choose the level of shine you would like to achieve.