I’m a student pilot right now! I’m at around 80% fluency too, and the stuttering is not an issue. I found it was tough in the beginning but got a lot better as I was saying the same phrases 90% of the time. It also helps to practice what you’re going to say to ATC before you fly. For example, my default phrase when I initiate contact with approach could be “Dayton approach, Aztec 702SP, 1 mile south of Farmersville, VFR”. Most of this phrase will stay the same every time I contact approach, except for the location. One issue that I can imagine occurring would happen when I go to receive my FAA medical. The current guidelines say issuing a medical to someone who stutters “requires FAA decision” and is on a case-by-case basis (https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/app_process/exam_tech/item28/amd/). I believe I’m fluent enough to pass this, but if you are worried, you can always get a medical before you start training. Another issue that I can see occurring would be taking the oral portion of the practical exam. However, I plan to mitigate as much stuttering as I can during this with enough studying/practice. I find that if I thoroughly know what I’m talking about, I’m more confident and stutter less.