"Cookie cutter" is a variation of tabletop construction that allows for slicing your plywood piece to raise or lower your track from the tabletop plywood. The biggest problem with the cookie cutter method is that you now have to support a different level of tabletop which may either partially or completely block (by supports) the train activity on your primary level. View blocking isn't a big issue with your plan, just something to think about.
Many modelers use a combination of L-girder and joist construction paired with tabletop construction used where it suits modeling purposes the most. Generally speaking, the whole layout is built using L-girders and joists, but in locations such as yards, engine terminals and large industries, a tabletop will connect to the joists.
"Spline" construction is primarily used as a track support by those who want to build their own curves without trying to cut them out of plywood supports. Typically, small strips of luan or masonite are glued together and then bent horizontally to support the track through a curve. I'm not sure how well spline works for vertical curves (inclines).
Chuck
