[intakexhaust]

Paslode nailer with soft bump end work fine. Tools are cheap to buy these days and I don't mean HF junk. CL, pawn shops are full of bargains.

Regardless, you can get by with cutting Hardie board using an ordinary circular saw, carbide blade 24T but used in REVERSE. You will need to wear a mask. Building a temporary saw jig / sled to support the heavy siding is another easy thing. Basically a 2 X 12 x 12 with a few 1 X 2 scraps nailed to the 2 X 12, and parallel and to width of the piece of siding. A guide bridge is made by having two pieces of 1 x 2 set 90 degree to the 1 X 2 scraps (above) and the circular saw simply is moved along the guide for perfect rep cuts.

James Hardie products are tops. I've worked alone with it but with some tricks to do so. I would highly advise to have a helper for the heavy siding. The homemade jig / sled is ideal for using up high on scaffold and plus have the stock temporarily up there.

BTW: Foam board razors and snaps clean. Should have no problem getting nice joints. Joints and seams with the proper and specific tape work just fine, quick and no messy spray foam. Good luck!