and welcome to the forum!
Hmm..that's a tough first question to ask.
I'm assuming that you use the word "professional" synonymous with "good enough to sell" here.
I've looked through your pictures and before I utter another word, I hasten to assure you that I'm no professional judge of the selling-potential of anyone's pictures.
That being said, perhaps some questions to ask yourself are:
1) Did the people in the pictures pay for them? A lot of people say "Oh, I'd pay for those" as a compliment, but would they really? If the answer is yes, you have a good start.
2) Can you produce pictures of this quality every time, all the time? With complete strangers you don't know? Can you churn out 25 per hour? Can you guide them to be comfortable and look their best in pictures of themselves? It's "easy" to say some flattering words to a pretty young lady that you already know and make her smile and try a little harder. But can you elicit that same response and make a stranger who may not feel as comfortable about his/her looks, to do the same..every time all the time?
3) Do you know enough to shoot successfully, consistently, under a wide range of circumstances? In poor lighting..a gray, rainy day?
I must apologize if it seems like I'm trying to discourage you. Nothing could be further from the truth. I see that you have gotten a lot compliments in your flickr stream already, which is encouraging, but ultimately not a true test of the question you are asking.
The real answer is that you don't know until you try it. Considering the astoundingly volume of - pardon my language - utter garbage photography that people are willing to pay for, it's not so much a question of some yardstick of quality to measure your images against. It's really more about whether you feel you are ready to throw yourself out there.
Like most artistic expressions, some will like your images and others won't. I personally like several of them and some of them, I like a lot. However, most of them share a certain common element - they are quite "heavy" with all the deep blacks/shadows. This is not a criticism - they have a contemporary urban feel..the streetlight orange hues and the deep shadows. But can you also make clear, crisp, light portraits of a family? Can you make "mature" shots that doesn't have that broody teensy vibe that is very pervasive in your flickr stream?
These are questions to answer to yourself, first and foremost. What kind of photography business are you trying to set up - a flexible one where the customers' wishes are met with a versatile talent. Or, one where they buy into your style and where you produce images according to your artistic vision - take it or leave it?
Either way, I wish you luck with whatever decision you choose to pursue. I'm hoping, and quite confident, that others here in the forum will pitch in with their own perspective on your question.
In many ways you ask a very brave question - opening yourself up to criticism from strangers about something that clearly has your passion. I'm also confident that the friendly nature of our fantastic forum-goers will not leave you too bruised after more responses