Those arms around the windshield are pretty vulnerable, and I have had the opportunity to do repairs 3 times on them. Your idea to remove the fairing is correct if you want to do the best job.
To start, if you can flex the crack a bit to fill it with CA glue. I use the stuff from the hobby shop that cures with a shot of catalyst. Put a bunch on the crack, work it in and then give is a shot. That will hold everything in place while you do the rest of the job.
On the back side remove the paint to at least 2 inches(3 would be better) away from the crack in every direction but not where it shows outside the inner trim. Rough up the surface with 36 or 80 grit.
Get some epoxy resin. About a half pint of resin with hardener should be about right. Fiberglass mat is messy to work with if you never did it before, but makes the strongest repair. I usually use tape, the bound edges make it easier to get a neat repair. Two inch wide should be good.
A note about resin. I used to use polyester, but learned that the material the fairings are made of has mold release wax in it that prevents a good bond. Epoxy, on the other hand bonds a lot better. The problem with epoxy is that it takes a lot longer to cure, and you have to arrange the work so you aren't putting the patch on a vertical surface. That really isn't a big deal, just position the fairing with the front pointing down. It will be a lot easier to work in that position as well.
Mix about two ounces of resin with catalyst, and let it sit for ten minutes while you cut the patches. Three layers is about right, with the top layer covering the entire roughed up area and each layer below it a bit smaller that the one above.
Put the patches on a scrap of plywood and saturate them with the resin. They;re ready when the fiberglass is transparent. Squeegee the excess resin out of the patches with a filler spreader before you put them on the repair. Start with the smallest patch and go up, pushing the air out with a chip brush before putting down the next one. Once they're all down, keep an eye on them to make sure they don't slide out of position. You might have to keep messing with them for as long as 4-5 hours. If the repair surface is horizontal, the chance of the patches sliding is almost zero.
When the patch has hardened, you can do the crack in the front. Get an old fashioned beer can opener and sharpen the point. Use it to widen out the crack to be about 2mm deep and 3mm wide. Even though it's polyester based, I have had good results with DuraGlas filler. Before you mix it and put it into the widened crack scrub out the inside of the crack with an old toothbrush dipped in acetone. Mix the DuraGlas and work it well into the crack. Build up the repair and after an overnight cure sand with 220 followed by 320. Use a block to get a fair surface. A scrap of wood will work. A couple coats of light gray high build primer sanded with 320 should have the surface ready for paint.
