Unless there are special ILS' in the USA, you shouldn't be selecting the lateral mode until you're inside the lateral and distance limits of the beam (eg 25nm). Certainly not until you are much closer than 40 miles. At 40 miles the glideslope is very unreliable. You should probably not select the vertical mode until you're within 15 miles and you certainly shouldn't be selecting it beyond 18 miles unless you're visual with the terrain. You might as well just select Approach at 160nm away at 40,000ft on a straight in approach with an agreeable approach controller.
The procedure might have minimum altitudes due to complex airspace arrangements in addition to terrain so you shouldn't descend below those until you're past the Final Approach Fix and on the GS. Unless I've missed something, isn't this all pretty standard/obvious? If I did, it's because it's late and i'm tired!