Is there a limit to how many SI you can have? Because I always see people talking about their one SI and I feel like I have at least four if not more but I'm hesitant to call them that because it seems atypical to me
You can have lots of SIs! While some autistics have one SI, many of us have multiple SIs. Some of us experience this as having a primary SI and then secondary ones. Others experience all of their SIs to the same degree. There are so many ways to experience SIs. Your experience is completely valid.
If it helps, I’ve had multiple SIs at the same time.