I apologize if this question has been asked before. I'm modifying Wings of Liberty(the official Blizzard campaign) and I'm not sure if it's possible to link maps in such a way that finishing a map prompts you to switch to the next one. If this is possible, can upgrades be added between missions, such as the Spear of Adun in Legacy of the Void?
You can do it offline. Check out any map project that includes a campaign launcher to see how it is done. For persistent upgrades between maps, look at tutorials on banks. They are text files that can be saved to the player's computer.