You might want to stick with Seaside. Especially if you are going to play several games in row. Not many people like playing all different cards for every one of their first 5 games -- it's too steep a learning curve to learn what all those cards do and begin to strategize well.
Your main goal the first game is to teach the basic mechanics and have fun. That's it. They're still getting used to the idea of building a deck. No Sea Hag (no Shelters, no Goons, no KC, no Knights, no cards not in the supply). No slogs. For whatever reason, the people I teach have no problems with durations, so they seem okay in a first game.
How about these pure Seaside kingdoms for the first two games (they share a lot of cards, but I think would play out pretty differently):
Bazaar, Explorer, Wharf, Caravan, Salvager, Cutpurse, Navigator, Warehouse, Smugglers, Pearl Diver
Bazaar, Treasury, Merchant Ship, Caravan, Cutpurse, Treasure Map, Island, Salvager, Fishing Village, Lighthouse
"High Seas" might be a good third game:
Bazaar, Explorer, Wharf, Caravan, Island, Pirate Ship, Lookout, Smugglers, Embargo, Haven
The other two recommended Seaside kingdoms would be good next. Then on to full random with in the expansion.
That should fill a night of Dominion easily.