I have resealed two side windows recently on our M. Relying on experience with my previous boat and a Demountable that sits on the back of my Nissan Navara which is glassfibre construction with perspex windows; also relying on an article in PBO a couple of years ago when as I recall they did some long term tests on various sealants; I was quite happy to use Sticks Like Sht. PBO found it nearly as good as the best sealants including Sikaflex. The price differential is extreme.
The windows are acrylic and are extremely strong whilst having an ability to flex with your glassfibre shell and I feel far more appropriate than glass. I would be tempted to go a size thicker than original as I feel the original windows flex a little too much in comparison with the deck.
Working with acrylic is extremely easy. It can be drilled with steel drills and cut with a tenon saw or a jigsaw, I prefer using a metal cutting blade with a lot of teath/inch to get a sufficiently fine cut. Edges can be rounded with a router or just sandpaper. Acrylic is provided with backing plastic which can be further protected with masking tape to ensure surfaces arent damaged when cutting. Mirror edges are easily obtained by using finer and finer sandpaper / wet and dry then finishing with very fine polishing paste, car Tcut is an option. There are plenty of YouTube guides on the subject. Acrylic is also brilliant for building things as the acrylic glue, like Airfix glues (remember building those brilliant Airfix kits) welds / melts the surfaces of the material to form joints when done well making them as strong as the material itself.