Peter,
I have had no issues with using the risers. I have added 1/2" foam to both sides ofthe risers to widen the roadbed area. This will give me the additional space needed for the foam roadbed and ballast I will be adding.
My switches are not on inclines, they are on flat sections of foam which cause no issues for the switches, just make sure you keep the switch machine level with the switch.
When I purchased all my subterrain items, I got the best prices here;
Hope this info helps.
Tim