I can't seem to be able to get the clothes shop to unlock. I had it unlocked once before but I started a new save after getting a new PC. I've progressed a bit further than I did in my old save now but I still haven't unlocked the clothes shop and no matter how often I visit the town plaza the tailor guy isn't showing up. Is there a specific point where the event to unlock the shop becomes available? And is it possible to miss it?
The main goal of the game is for Celica to become a powerful mage who can use her magic on monsters of varying strength. This requires alchemy, skill development, increasing mastery level, and using artifacts. If you maintain this balance, then there are usually no problems.
In your case, it seems that you forgot to help Celica learn skills. As soon as she learns a few, the tailor will come to the square (plaza).
The Agranor library contains books with tips for beginners and how to gain skills.