Linen Micarta will work well and sand evenly with the other materials. Bone may be a problem with staining from the dark woods in sanding. Plastics and things like Alumilite may be too soft and want to undercut when sanding. For wood, stabilized holly is nice. I'd be glad to send you a block or two if you go that route.
Whatever you choose, use a liner strip under the assembly or it will break apart eventually. Glue up the segments on the liner with a slow-cure epoxy. After a 24-hour cure, cut the shape needed from it. (see tip below)
G-10 is a very good choice for the liner. The liner should be between .030" and .060" thick.
120 grit is a perfect surface for gluing everything up.
TIP:
A neat trick for making perfectly matched segmented scales is to assemble the pair of scales larger than needed, say 2X6". After gluing the segments on the liners and letting them cure, sand the long sides on both to expose the segment lines clearly. Use double sided tape (the kind wood turners use) to place them back-to-back so the segments are aligned with each other. Use spray adhesive to stick the handle template drawing on the top, or draw it on, and bandsaw out the rough scales. Drill the rivet/bolt holes and temporarily install the bolts/rivets while still taped together. Now you can pre-shape the block as needed to get close to the tang shape, and finish the front end where the ricasso will be.
When taken apart you will have a perfectly matched set of assembled scales ready to mount on the tang and finish shaping.
Plusses for this method - You only have to make the two pieces for the center segment the same width. The simplest way to do that is make a longer piece, sand the back and long sides flat to 120 grit, and cut it in half. This will make two identical width center pieces ready to assemble. The front and back pieces can be random shape, as long as they have one straight edge to glue to the center strip. Again, the best way to make them match is to make longer pieces, sand the back and mating edge flat, and cut in half. Once glued up and temporarily bolted/riveted together the entire profile will be cut as one piece, making two identical reversed scales. Depending on how wide you make the starter laminates, you can angle the handle template on the block to make the center segment angled. Lay it out on paper to figure the width needed for your desired angle.
Once you understand the method of doing it this way, you will probably make the initial lamination as one wide scale and cut it in half.
I'll make myself a note to do a tutorial on this. It is ten times easier to see than to write.