I would personally avoid suggesting any hardware at this point for the following reasons. I think that the whole premise for the discussion is flawed because the focus from the start has been on buying a camera body - always a trap for young players.
We have little idea the OP's situation apart from a their statement "I am obviously a beginning photographer, but hope to make a side career out of it in the future", and that they have an Rebel T5. We have no idea what lenses they have, or what they intend to do in terms of the kinds of images they hope to generate - or to put it another way, what are they going to shoot? That has a huge impact on lens selection, and arguably even the sensor size. "Professional" identifies with a wide range of activities from large, high quality traditional prints to people posting reduced images on the web. So again knowing the input and output are very helpful.
The only thing we DO know is that they are new and in the middle of a photography course. As Bob, Bill and I have said the best things they can do is to finish the course, take a lot of photos and learn from them. I also recommend spending a lot of time studying the composition of great photographers and painters who practice in the genre in which they have an interest *whatever that is".
Finally, the question of cost/benefit come in. What is the market like in the area in which the OP lives and wants to work?
Is it saturated with competition or pretty open. These days it is more likely to be the former. What sort of gear is generating the work that he is interested in? As Ernie says customers will want professional-quality products, and that means decent gear - something that $700 will not touch if it is to include the glass.
Let me make myself absolutely clear - I am not saying that the OP will never upgrade (that would be silly), I am saying that right now, with limited knowledge and budget this is not the time invest money in gear. It's time to invest effort into learning the basics of good photography, both the technique of using cameras and the art of composing great images - and then there is post production to master. That can be done with the camera body they have - we have had no information provided about lenses so it's hard to comment on that one, but one can still compose great shots on a less than ideal lens. Better to further their education and experience, take on free jobs for friends and small businesses to get some idea of how to be a professional - better still to learn WITH a professional as an assistant if they will let them.
The following image was taken on an EOS 600D (Rebel T3i), vintage 2011, using the EF-S 60mm macro lens (2005) and much reduced to post here.
The family love this photo of their patriarch - I am not a portrait photographer, and I took it because he is a friend, but his family wanted to pay for it (I declined) because they felt it captured his essence. If I was planning to make large, detailed prints of this to sell, I would have used more professional equipment, but it was just a casual moment.
I'm not posting this to say "I'm great look at me", I'm posting it to say that older gear can render results if it is used with experience, and certainly can be sufficient to hone one's skills upon.
