I'd love to help but I lack of time to get involved in any other project. Hope you the best for your shop

tbh a good idea is not what's the most important imo. You can peak one that you like and just hire a good marketing team this is how things works in real life

I would definitely recommend you to organize some contest for more creative T-shirts. Maybe just see what your competitors are doing. No offense here but I found them not funny and a bit too much cliche

Sounds pretty fair
Out of curiosity, which token are you giving away to your users?
I can offer Greek translation if you're interested.
Hope you the best for your project

Very good idea indeed, hope your project get adoption

Sounds promising indeed + very positive signal that you funded this project for this reason!