If you don't have TP, no way to get to Nighon without moving through the Connecting Tunnels again. If you know the way through the Tunnels, I guess it's not all *that* long, but it's long enough.Off the top of my head, it MAY be possible to do everything you want in Nighon in one visit, then go into the Eeofol tunnel & portal back from Eeofol, and not have to visit Nighon again. But your party needs to be pretty advanced for the Maze (and *really* advanced if you want to clear everything on the map & take on the Megadragon). So you'd be leaving Nighon until quite late.
If you want TP without taking a Sorceror, Archer and Druid can both get Water Magic to Master level. Druid could also be your backup healer, although to answer your question I've played the game with a single Cleric as healer many times. Ypu just need scrolls/potions for the times your Cleric goes down. And ALWAYS keep Regeneration active!
Of course, you could also just hire a Gate Master every time you wanted to get back to Nighon
