Still learning more about nodes, with some tips from hellrazor. Been put into practice and tested in the nearly complete very large USO (pictured). Still rechecking and adding to the vanilla variations. On the new USOs, I've been looking at the missions and the number of times each USO/UFO class can appear as a wave:
Probe: Survey, Escort, Cruiser
Interdiction: Survey, Survey, Escort, Cruiser, Cruiser, Hunter, Hunter, Dread
Resource Raid: Survey, Escort, Cruiser, Heavy cruiser, Heavy cruiser
Infiltration: Survey, Escort, Escort, Cruiser, Cruiser, Battleship, Supply, Dread
Alien base: Survey, Escort, Cruiser, Supply, Dread
Surface attack: Escort, Cruiser, Battleship, battleship
Retaliation: Survey, Escort, Cruiser, Dread
Supply: supply
Or in terms of how many times a USO/UFO will appear as a unique wave:
Survey: 7
Escort 8
Cruiser 9
Hunter 2
Heavy cruiser 2
Battleship 3
Supply 3
Dread 4
Assuming you wanted to keep the number of UFOs/USOs the same and similar enemy/loot numbers, a really ambitious new ship mod could replace each of those occurrences with a unique ship. Or to put it another way, each mission has it's own unique ships. The hunter and heavy cruiser already only appear on their specific mission. Now I won't go that far but it's a good guide for what kinds of new ships to make. More cruiser sized ships basically, and some escort sized ones if I can think of enough things to do with that small space.