An SVG is an image. I’m sure I’ve seen an SVG importer for JME somewhere. To that end it would be a texture that you can project on to any geometry, including a quad.
You scale things using .setScale. “To the right dimensions” is a bit vague. Only you will know the dimensions of the model, so only you will know how much to scale it by. Having said that, there is a bounding volume that will tell you the smallest extents from its center.
For height maps, there are many implementations available. It’s not too difficult to “roll your own” either. I have written an implementation myself.
For mine it wants a height map size +3 bigger than the size of the generated mesh. 1 for the extra vertex at the end, and +1 for each side so it can calculate the edge normals correctly and join without normal seams.