Everyone says my product is cool. Is it a good reason for a startup?

Only you can answer this question, especially without showing your product. As a rule of thumb, when you have idea/product, use this early version as an MVP, try to soft-market it to a small circle of pelple, be it your friends, or people in your living area. Get their feadback. If overwhelmingly positive, make it a startup slowly, and iterate from there. If not positive, but not negative, add some more features from the feedbacks, or completely change it, make a statup. If completely negative, dong' give up yet. Using the same idea, pivot towards a completely NEW(but similar) product. Always iterate!

Probably not. If people you speak with commit time/reputation/money then it’s a much stronger signal.

Your product is cool. Now what? How would you monetize it, or sell it?

If you did, what's the competition like? Can you carve out a niche for yourself?

...Now that you're properly discouraged - can you overcome all those challenges? If you can, calculate how much effort(look: money) it would take to do make your product into a money-making product; something you can sell...

...And then decide whether it might just be worth trying, even if the chances are small, even if you need to buckle up and work like a horse.

It's cool when it's free. Will they actually pay is a different question. Lots of people bash products they still pay for so...

They like it but are they using it? Do they like it so much they tell other people about it?