All good advice from Amitygravel. And yes, a jigsaw with a fine tooth blade works fine as long as the FRP is supported near the cut line so it doesn't flap and crack. Scoring and snapping isn't very effective, you'll likely crack it. I have been using my oscillating multitool to cut it lately, with a round type flush cutting bimetal blade. Goes through it like butter and it's easier to carry around than the jigsaw. And since the blade travel is very low, there's less risk of it grabbing and cracking a piece that's not fully supported.
In addition, since I see you're in Michigan like me... best to apply it in warm temperatures. The troweled-on adhesive doesn't like cold temperatures when curing.
For small pieces, I have been using 3M Super90 spray adhesive. Don't even think about using it on a piece that you aren't certain you can position in one try with no sliding, but the Super90 is very strong and sets up nearly instantly. I like it for small pieces that I know I can put in place without having to slide them into position.
The Liquid Nails FRP adhesive (FRP-310) from Home Depot works well. I'd advise opening the bucket at the contractor's desk before leaving the store though. Two 3.5-gallon buckets I bought this winter were bad and I didn't know it until I opened them at home. Looked to me like they had frozen and rethawed many times, and the adhesive was useless. I had to return them.
Note that it's inadvisable to use the adhesive on painted walls. In the spots where I went over painted drywall, I sanded, applied two thin coats of primer and scuff sanded before troweling on the adhesive. It has held up fine so far, with some fairly brutal temperature cycling. It's not recommended for exterior applications, but it's been fine in my currently unheated garage. Heater goes in later this year.
