You asked about risers, here are some suggested ways to develop risers.
In building bench work my pattern for years has been to use Russian Birch 23/32". However in recent years I have been using other materials harking back to earlier stressed skin construction.
I get 13 three and a half inch wide by eight foot long strips which is great for cross members and up rights.
For up rights or risers one way is to use 6.0mm lauan gussets on each side at the base to fasten it on to a cross member. They are shot on over TB-III with a 1/4" crown stapler.
For the top of the upright I add a plywood "L" bracket cut at the same degree as the incline and fasten to the upright.
Another way, you could also cut the cross members and risers out of a slab of plywood as seen in the next two photos.
You may balk at the apparent waste but trust me, the scrap will be used in many other aspects of layout construction
Even without using curved side frames dramatic topography can be made into modules.