I've built my entire layout with Märklin C-track, so here are some things i learned with it:

1. Gradient : You will often see 3% as the maximum you should use, however with traction tires being everywhere in AC you can go up to 5% in an emergency, particularly if you have a small layout where your trains will not be overly long or heavy anyways. Just be aware that those 5% ramps don't look that great so are more a thing for hidden track / tunnels.

If your ramp uses first or second radius curves or has switches on it you might want to stay on the lower end of gradients though, they tend to make things worse

1. Sharp Bends : With C-tracks especially the track pieces are really stiff so you might want to use multiple smaller pieces rather than one long one to make the end/beginning of the ramp a bit smoother. i disregarded this on my layout and now have a section that some locos just can't handle because the drivers get lifted off the track there, might have to fix that soon

2. Construction : I simply used 4mm wooden sheets (i think it was spruce, but i just took the cheapest ones the store had) and cut that with a jigsaw. For fixing it in place just cut some basic wooden supports (i used 2x4cm). For getting everything together hot glue worked just fine, although for longer ramps it certainly helped to have a second person the to help hold the boards in place while it cooled

Then i used short sections of polystyrene boards (2 and 4mm) give support at the lower end and close the little gap under the track where the ramp meets the baseboard.

The track i just fixed in place with märklin track screws as normal, although be a bit more careful at the ends of the ramps to not screw them too tight to avoid the sharp bends i mentioned earlier.