hey dude ;-)
borrow me a server with infinite computing power and tommorow its yours ;-)
back to your question: i guess it should be under 2GB when using strm3 source.
What I mean.
When its possible to overlay a vector contour map (with its own theme) on the fly in locus (on top of normal osm vector maps with another theme), why should you / or menion need to create maps that includes osm data and contour data in one map anymore?
Contours don't change. They could be created once, be put on the server. Users have to download them only once.
OSM data changes. Maps have to be recreated. Users have to download them again.
And the creation for a contour only map should be a lot faster then a map with osm+contour data?