BTW, the floor polish in question is a product called Future in the US. It is an acrylic floor polish. In other countries, it is known by other names, such as Johnson's Kleer, but it is essentially the same product. I know many modelers that use the stuff for clearcoating models with an airbrush, but I just use it for dipping canopies and use other products for clearcoating since Future can be removed by cleaners with ammonia in them, such as Windex (keep windex handy to strip the Future off if you make a mistake in applying it).
For sanding the area out, I start with about 320 grit and then go with progressively finer grits to bring back the luster before Future coating the part. The highest that 3M
sandpapers go is 600 grit, but many shops that carry model cars also carry a set of polishing cloths that start at about 1200 grit and go up to 14000 grit. These were originally intended for polishing optics, but they work great for polishing paintjobs (which car modelers use them for) and polishing canopies. If you don't have access to those, then after polishing the area with 600 grit, use some toothpaste as the final plastic polish before dipping the part in Future.
BTW, the clear side windows found on many 1/144 airliner kits are pretty thick and a lot of modelers I know either fill the windows completely and use aftermarket window decals or they fill the window ports with a product called Microscale Krystal Klear (no relation to Future). This is a white glue product that can be stretched over small open areas with a toothpick and when it dries it takes on the appearance of a window. If it doesn't work, it can be stripped off easily and done again. Most every good hobby shop in North America (and some in Europe) tends to stock this product and it also works well for attaching canopies as it is essentially a white glue product.
For models that are 1/100 and larger scale, clear windows look better then decals.